SSC CHSL 2021 PYQ — Question 62

The correct answer is option 1 i.e. 7 hours

Let the speed of Mohan and Kishore is x km/hr and y km/hr, respectively.

According to the given question,

${63 \over x} - {63 \over y} = 2$ ⇒ 63y - 63x = 2xy   ....(i)

Also, the new speed of Mohan = ${150 \over 100} \times x$ = ${3 \over 2 }x$

⇒ ${63 \over y} - {63 \over {3 \over 2}x} = 1$ ⇒ ${63 \over y} - {42 \over x} = 1$  ⇒ 63x - 42y = xy   ..(ii)

Adding equations (i) and (ii), we get

⇒ 21y = 3xy

⇒ x = 7

⇒ y = 9

Time taken by Kishore to travel 63 km = $63 \over 9$ = 7 hours.