Defendants Terry Quarles and Lamont Brown appeal their convictions of conspiring to possess with intent to distribute in excess of fifty grams of cocaine base (“crack”). Brown also appeals his conviction of possession of crack with intent to distribute. Both defendants attack the District Court’s1 denial of their motions to suppress evidence seized during two separate stops of automobiles involved in the events leading to their arrests. Quarles raises additional issues relating to his trial and sentencing. We affirm.
I.
On June 6, 1990, & reliable confidential informant told the St. Paul police that Brown and Quarles had received a large quantity of crack and would be making deliveries that afternoon in a white Cadillac driven by either Brown, Quarles, or a juvenile named Ogean Pruitt. Each of these individuals is a young black male. On the basis of this information the police put several surveillance teams in the Summit-University area that afternoon. At about 4:15 p.m. one of these teams saw a white Cadillac, driven by a young black male, enter a short side-street that ends in a parking lot. The police had estimated a vehicle would only take thirty to forty seconds to traverse this street; although they temporarily lost sight of the white Cadillac, they saw it reappear about five minutes after it had entered the street. They then stopped the vehicle.
The driver was identified as Ogean Pruitt and placed under arrest. A search of the Cadillac produced four grams of crack along with some hotel keys, one of which was a key to Room 30 of the Midway Motel. During this search, Quarles appeared on foot and asked what was going on. When the police informed him that *500Pruitt had been arrested, Quarles told them he owned the Cadillac and asked if he could have the motel keys. The police refused and Quarles left.
At about 5:00 p.m., Officers McNeely and Cooper arrived in plain clothes at the Midway Motel. They had been directed to secure the area until a warrant could be obtained to search Room 30. Both officers were given all available intelligence regarding the possible receipt of a large quantity of crack by Quarles and Brown as well as the details of Pruitt’s arrest. The motel’s manager told the officers that Room 30 had been vacant since June 3 and consented to a search of the room.
Nothing was found during this search, after which Officer Cooper went to the motel’s office to review telephone records for the room while Officer McNeely waited outside in their unmarked cruiser. A short time later Quarles entered the motel’s office and spotted a police radio Cooper had left on the front desk. Cooper testified that Quarles appeared to be very nervous and began backing out of the office. When Cooper asked if she might help him, Quarles asked at what age a person could rent a room and backed out the office door.
McNeely, who recognized Quarles from a previous contact, watched him exit the office and approach two other men who were walking towards Quarles from a bronze Cadillac. One of those men later was identified as Brown. As the three conversed, McNeely overheard Quarles say something about “cops.” Immediately, the officer radioed for a backup, got out of his car and identified himself. Quarles and Brown stopped, but the third man began walking away from the motel. McNeely went after the third man and ordered him to stop. While McNeely was thus occupied, Quarles and Brown attempted to drive off in the bronze Cadillac. McNeely went after the pair, ordered them out of the car, and asked for identification. With McNeely busy with Quarles and Brown, the third man again attempted to leave the motel area. At that point officers Flaherty and Scott arrived. McNeely told them to watch Quarles and Brown and again went after the third man.
As McNeely turned to pursue the third man, Officer Flaherty saw Brown reach into his pants. Flaherty suspected that Brown may have been reaching for a weapon; the officer rushed Brown, placed his hands on the Cadillac, and performed a “pat-down” search. Flaherty felt a hard lump, reached into Brown’s pants and pulled out a quantity of cocaine that was found to weigh 210 grams. Both Brown and Quarles then were arrested and later were indicted on the charges at issue in this appeal.
Prior to their trial, Brown and Quarles moved to suppress the evidence seized during the stops of the Cadillacs. After a hearing, the magistrate2 found the stop of the white Cadillac was a valid investigatory stop; the officers had probable cause to arrest Pruitt; and the subsequent search of the Cadillac was valid as incident to Pruitt’s arrest. With respect to the bronze Cadillac, the magistrate found McNeely had a reasonable suspicion to order Brown and Quarles to stop the car and identify themselves; the two were not initially under arrest at the time of the stop; and Officer Flaherty was justified in searching Brown’s pants after Brown appeared to reach for a weapon. Based upon these findings, the magistrate recommended that defendants’ motions to suppress be denied. The District Court adopted the magistrate’s findings and denied the motions.
A jury found Brown and Quarles guilty of conspiracy to possess crack with intent to distribute. Brown also was convicted of possession of crack with intent to distribute. Quarles was acquitted on the possession charge. Both defendants appeal, reasserting the arguments they advanced in support of their suppression motions. Quarles also challenges an instruction to the jury; the sufficiency of the evidence; an alleged inconsistency between his con*501spiracy conviction and his acquittal on the possession charge; and the calculation of his sentence.
II.
Quarles contends that the evidence obtained during the search of his white Cadillac should have been suppressed because the stop was not supported by reasonable suspicion and because the resulting search was not incident to a lawful arrest. “Reasonable suspicion may be based on an informant’s tip as long as it is sufficiently reliable.” United States v. Thompson, 906 F.2d 1292, 1295 (8th Cir.), cert. denied, — U.S. -, 111 S.Ct. 530, 112 L.Ed.2d 540 (1990). Here, the tip on which the police were acting not only came from an informant known by them to be reliable, but also was substantially corroborated when the surveillance team observed a white Cadillac, driven by a black male in the Summit-University area, taking an unreasonably long time to travel through a short street. In these circumstances, it was reasonable for the police to suspect that the white Cadillac was involved in the cocaine delivery scheme to which the informant had alerted them. Their justifiable stop of the white Cadillac revealed the driver to be Pruitt, one of the individuals identified by the informant. These circumstances provided the officers with sufficient probable cause to arrest Pruitt. “[WJhen a policeman has made a lawful custodial arrest of the occupant of an automobile, he may, as a contemporaneous incident of that arrest, search the passenger compartment of that automobile.” New York v. Belton, 453 U.S. 454, 460, 101 S.Ct. 2860, 2864, 69 L.Ed.2d 768 (1981) (footnotes omitted). The cocaine base discovered behind the radio in the white Cadillac’s dashboard, the motel room key found on the front floorboard, and the other items found in the car3 were products of a lawful search incident to arrest. The District Court did not err in denying Quarles’s motion to suppress this evidence.
III.
Brown argues the cocaine base found in his pants should have been suppressed because the search resulted from an invalid stop of the bronze Cadillac and an illegal seizure of his person. We disagree. If a law enforcement officer has reasonable suspicion that criminal activity “may be afoot,” Terry v. Ohio, 392 U.S. 1, 30, 88 S.Ct. 1868, 1884, 20 L.Ed.2d 889 (1968), he may stop and briefly detain individuals for investigative purposes. United States v. Brignoni-Ponce, 422 U.S. 873, 881-82, 95 S.Ct. 2574, 2580, 45 L.Ed.2d 607 (1975). Reasonable suspicion is based on “specific and articulable facts,” Terry, 392 U.S. at 21, 88 S.Ct. at 1880, which are considered collectively and “in light of the significance that a law enforcement officer experienced in detecting criminal activity would attach to them.” United States v. Turpin, 920 F.2d 1377, 1385 (8th Cir.1990), cert. denied, — U.S. -, 111 S.Ct. 1428, 113 L.Ed.2d 480 (1991).
At the time Officer McNeely attempted to detain Brown, he was aware of the reliable informant’s tip that Brown and Quarles had obtained a large quantity of crack that morning and would be making deliveries that afternoon. The officer also knew that Quarles’s car had been stopped earlier that afternoon and had been found to contain a small amount of crack and a key to a room at the Midway Motel. The officer had observed Brown and Quarles arrive together at the motel and had overheard their conversation concerning “cops.” When McNeely stopped Brown, the defendant attempted to flee with Quarles in the bronze Cadillac. These circumstances justify McNeely’s investigatory detention of Brown.
Because McNeely’s stop was valid, Officer Flaherty’s decision to frisk Brown to determine if he was armed was permissible, Turpin, 920 F.2d at 1385 (citing Terry, 392 U.S. at 27, 88 S.Ct. at 1883), especially since Flaherty saw Brown put his hands *502inside his pants. Flaherty detected a hard lump that might have been a firearm; he was justified in reaching into Brown’s pants to determine whether Brown possessed a weapon. Because this search was valid, the District Court correctly denied Brown’s motion to suppress.
IV.
We now turn to Quarles’s remaining claims, which relate to the 210 grams of crack seized from Brown. Quarles reasons that the weight of the crack is an element of the crime with which he was charged, namely, conspiracy to possess with intent to distribute in excess of fifty grams. Quarles argues the government failed to produce sufficient evidence to sustain his conviction because the 210 grams were found on Brown and only four grams were found in Quarles’s white Cadillac. In this connection, Quarles also argues there was no direct testimony as to the amount of crack found on Brown.
We review the evidence in the light most favorable to the government, which includes giving it the benefit of all reasonable inferences. United States v. Temple, 890 F.2d 1043, 1045 (8th Cir.1989). Although the government did not ask any witness the exact weight of the crack found on Brown, the crack so found was admitted into evidence, its exact weight (210.7 grams) was established, and it was identified as the cocaine base Officer Flah-erty took from Brown’s pants. There is testimony that possession of 210 grams of crack cocaine is inconsistent with personal use and that Quarles had learned shortly after his arrest that the amount seized from Brown was 210 grams. There is also ample evidence from which the jury could infer the existence of a conspiracy between Quarles and Brown to distribute this cocaine base. Quarles’s attack on the sufficiency of the government’s evidence is unavailing.
Quarles claims the jury instruction with respect to the conspiracy charge was ambiguous because it did not clarify that the cocaine at issue was the larger amount found on Brown rather than the four grams found in Quarles’s white Cadillac following Pruitt’s arrest.4 Quarles speculates that this ambiguity may have resulted in his being convicted of an uncharged crime, namely, conspiracy to possess with intent to distribute the smaller amount of cocaine base. He claims the acquittal on the possession count “significantly bolster[s]” his contention that the jury found he “was unaware of the cocaine which Brown was carrying but he was aware of the cocaine in his car which was driven by Pruitt.” Appellant’s Brief at 22. Quarles extends this line of reasoning to argue that because there was “no factual basis upon which the trial court could properly conclude that the amount of crack cocaine with which [he] was convicted was 210 grams,” Appellant’s Brief at 31, the District Court erred in using this amount to calculate his base offense level for sentencing purposes.
Quarles’s exercises in speculation are not persuasive. We have concluded the evidence presented was sufficient to sustain his conviction of conspiracy to possess with intent to distribute in excess of fifty grams. In addition, we are satisfied the jury was not misled as to the amount of crack in issue. Throughout the trial, the government’s case focused on the 210 grams found on Brown, not the four grams found in Quarles’s white Cadillac. We therefore cannot agree with Quarles’s claims regarding the allegedly ambiguous jury instructions, the significance of his acquittal on the possession count, or his sentence. Having carefully reviewed the record, we are convinced it fully supports Quarles's conviction and sentence.
Judge Bright’s concurring and dissenting opinion, arguing that Quarles’s case should be remanded for resentencing, seeks to apply a new approach based on views expressed in a now-vacated opinion from the Sixth Circuit, United States v. Davern, 937 F.2d 1041 (6th Cir.1991), va*503cated, reh’g en banc granted. Even if we thought the vacated opinion in Davem persuasive, we do not agree with Judge Bright that the jury’s findings with respect to Quarles were inconsistent. A conspiracy conviction under 21 U.S.C. § 846 does not require proof of an act in furtherance of the conspiracy; the statute only requires proof that the defendant “entered into an agreement with at least one other person and that the agreement had as its objective a violation of the law.” United States v. Foote, 898 F.2d 659, 663 (8th Cir.), cert. denied, — U.S. -, 111 S.Ct. 112, 112 L.Ed.2d 81 (1990); see also United States v. Covos, 872 F.2d 805, 810 (8th Cir.) (holding that section 846 does not require proof of an overt act in addition to proof of an agreement), cert. denied, 493 U.S. 840, 110 S.Ct. 124, 107 L.Ed.2d 85 (1989). In contrast, a conviction for aiding and abetting requires proof of some act done in furtherance of the conspiracy’s purpose. Foote, 898 F.2d at 664. Therefore, assuming ar-guendo that an arguably inconsistent verdict were a mitigating factor that a sentencing court could take into account, no such verdict was reached in this case. United States v. Fesler, 781 F.2d 384, 390 (5th Cir.), cert. denied, 476 U.S. 1118, 106 S.Ct. 1977, 90 L.Ed.2d 661 (1986). We similarly reject, for the reasons adumbrated above, Judge Bright’s suggestion that the District Court lacked a sufficient evidentia-ry basis for attributing to Quarles, for sentencing purposes, the 210 grams of crack found on his co-conspirator Brown.
V.
For the reasons stated, the convictions and the challenged sentence are affirmed.
. The Honorable Harry H. MacLaughlin, United States District Judge for the District of Minnesota.
. The Honorable Franklin L. Noel, United States Magistrate Judge for the District of Minnesota.
. These other items included some cash, a pager, and a bill of sale showing that Quarles had paid cash for the Cadillac.
. The record shows Quarles did not object to the instruction when it was proposed or when it was read to the jury. Because he failed to object, his conviction may be reversed only if there is plain error. United States v. Kragness, 830 F.2d 842, 855 (8th Cir.1987).