Question

Walking at 4/7th of your usual speed, you will reach the school 15 min late. What is the usual time taken by you to reach your school?

• A. 40 min
• B. 20 min
• C. 30 min
• D. 15 min

Answer 1

The correct option is B

20 min

We know that Speed = $\frac{Distance}{Time}$.

or, Distance = $Speed\times Time$

Here, distance traveled is same( from your home to school), So, More the speed, less the time taken(speed and time have an inverse relation if the distance of travel is same).

So, here, usually, D = $S\times T$

Also, D = $\frac{4}{7}\times S\times T^{\prime }$, ( where T' = T+15, late by 15 min)

So, D = $S\times T=\frac{4}{7}\times S\times (T+15)$

7T = 4T + 60

On solving we'll get, T = 20 min