question:A 600 meter long train crosses a signal post in 40 seconds. How long will it take to cross a 3 kilometer long bridge, at the same speed?
Options:
(A) 4 min
(B) 8 min
(C) 9 min
(D) 6 min
(E) 1 min
answer:(A)
Stream of consciousness:S = 600/40 = 15 mps
S = 3600/15 = 240 sec = 4 min


question:In a certain animal population, for each of the first 3 months of life, the probability that an animal will die during that month is 1/10. For a group of 600 newborn members of the population, approximately how many would be expected to survive the first 3 months of life?
Options:
(A) 438
(B) 446
(C) 452
(D) 462
(E) 470
answer:(A)
Stream of consciousness:Number of newborns that can die in first month = 1/10 *600 = 60
Survived = 540
Number of newborns that can die in second month = 1/10 * 540 = 54
Survived = 486
Number of newborns that can die in third month = 1/10 * 486 = 48
Survived = 438


question:How long does a train 110 m long traveling at 60 kmph takes to cross a bridge of 390 m in length?
Options:
(A) 18.9 sec
(B) 88.9 sec
(C) 22.9 sec
(D) 30.00 sec
(E) 72.0 sec
answer:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
(D)
Stream of consciousness:D = 110 + 390 = 500 m
S = 60 * 5/18 = 50/3
T = 500 * 3/50 = 30 sec