Question

Points A and B are 70 km apart on a highway. A car starts from A and another car starts from B simultaneously. If they travel in the same direction, they meet in 7 hours. But, if they travel towards each other, they meet in 1 hour. Find the speed of each car.

Answer 1

Let X and Y be the cars starting from points A and B, respectively and let their speeds be x km/h and y km/h, respectively.
Then, we have the following cases:
Case I: When the two cars move in the same direction
In this case, let the two cars meet at point M.

Distance covered by car X in 7 hours = 7x km
Distance covered by car Y in 7 hours = 7y km
∴ AM = (7x) km and BM = (7y) km
⇒(AM – BM) = AB
⇒(7x – 7y) = 70
⇒7(x – y) = 70
⇒(x – y) = 10                          ……..(i)
Case II: When the two cars move in opposite directions
In this case, let the two cars meet at point N.
Distance covered by car X in 1 hour = x km
Distance covered by car Y in 1 hour = y km
∴ AN = x km and BN = y km
⇒ AN + BN = AB
⇒ x + y = 70                         ………(ii)
On adding (i) and (ii), we get:
2x = 80
⇒x = 40
On substituting x = 40 in (i), we get:
40 – y = 10
⇒y = (40 – 10) = 30
Hence, the speed of car X is 40km/h and the speed of car Y is 30km/h.