1. Points A and B are 70km. 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 7hrs, but if they travel towards each other, they meet in one hour. Find the speed of two cars. Solution: Let’s consider the car starting from point A as X and its speed as x km/hr. Two cars traveling at 62 km/hr and 54 km/hr respectively, left Town A for Town B at the same time. The faster car passed on oncoming truck 10 hours later. Time taken is 1 hour. Let x be the speed of the truck.Since they are travelling in the opposite direction, the relative speed will be 54 + x.

The front of train $1$ has to travel the total length of both trains before the crossing is done, so the time it takes is $\frac {d_1+d_2}{v_1+v_2}$. With this correction your approach is correct. With this correction your approach is correct.