Two sisters Neha and Monica walk to school from the house. Neha takes 40 minutes while Monica takes 30 minutes. One day Neha started 5 minutes earlier than Monica. In how many minutes would Monica overtake Neha?

The distance covered by both Neha and Monica is same .
Now Neha takes 40 minutes to cover the distance which Monica covers in 30 minutes
So we can say their speed ratio = 3:4
Let speed of Neha be 3v and speed of Monica be 4v
Now in 5 minutes Neha would cover 15v of distance
Now Neha is ahead by 15v when Monica starts
so relative distance = 15v
And relative speed = 4v-3v =v
Therefore time to overtake = 15v/v = 15minutes