Re: The road between town A and town B is 500 miles long. John drove direc
[#permalink]
21 Mar 2022, 21:14
1) At the point of crossing :
john averaged a speed of = 200 /5 = 40 mph
Jane averaged a speed of = 300/5 = 60 mph
but their speed after they cross is unknown
John could slow down close to 0 mph and jane could drive at 70 mph hence jane arriving before john (reverse situation also possible)
Thus 1 alone Not sufficient
2) Jane averaged 60 mph implies that jane will take 500/60 hours to reach A
Can john do better ?
yes if for example john speed is 65 mph then john will arrive first
No if for example john's speed is 55 mph then john will arrive after jane
Thus 2 alone Not sufficient
1) and 2)
After crossing john, jane is still averaging 60 mph implies that jane will take 200/60 = 20/6 hours to reach A
so is john going to arrive at B before or after Jane arrive at A knowing that john should never go above 70mph anytime ?
The time john will take to arrive at B is 300/x where x is john's average speed.
So we must determine if that time can be smaller than 20/6 (jane's time to reach A) without breaking the limit of 70mph ?
if 300/x < 20/6 => x>90 mph (not possible because it shows that john will have to break the 70 mph limit if he wants to reach B before jane's reaches A)
Then the only option is that john will not arrive before Jane
Sufficient
hence C is the answer
Thanks to comment my strategy of reasoning !