In covering a distance of 90 km, Anirudh takes 8 hours more than Burhan. If Anirudh doubles his speed, then he would take 7 hours less than Burhan. Anirudh's speed is:

Correct option is A

Given:

Distance D = 90 km
Anirudh takes 8 hours more than Burhan

If Anirudh doubles speed, he takes 7 hours less than Burhan 

Formula Used:

Time = $$\frac{Distance} { Speed}$$​​

Solution:

Let Anirudh's speed = x km/h

Burhan's speed = y km/h

​$$\frac{90}{x} - \frac{90}{y} = 8 \quad (1)$$​​

​​If Anirudh doubles speed, time taken is $$\frac{90}{2x} = \frac{45}{x}$$​​

So:

​$$\frac{45}{x} - \frac{90}{y} = -7 \quad (2)$$​​

From (1):

​$$\frac{90}{x} - \frac{90}{y} = 8$$​​

Subtract (2) from (1):

​$$\left(\frac{90}{x} - \frac{90}{y}\right) - \left(\frac{45}{x} - \frac{90}{y}\right) = 8 - (-7)$$​​

​$$\frac{90}{x} - \frac{90}{y} - \frac{45}{x} + \frac{90}{y} = 15$$​​

​$$\frac{45}{x} = 15$$​​

​$$x = \frac{45}{15} = 3 \text{ km/h}$$​​