SSC CGL 2022 PYQ — Question 60

The correct answer is Option 4. i.e. (25y²  + 5y + 1) km/h.

Given:

Distance = (125 y³ - 1) km

Time = (5y - 1) hours

Concept Used:

Distance = Speed × Time

a³ - b³ = (a - b)(a² + ab + b²)

Explanation:

Speed of train = $Distance \over Time$

⇒ Speed of train = $(125 y^3 - 1) \over (5y - 1)$

⇒ Speed of train = ${(5y)^3 - 1^3} \over (5y - 1)$

⇒ Speed of train = ${(5y - 1)(25y^2 + 5y + 1)} \over (5y - 1)$

⇒ Speed of train = 25y² + 5y + 1

Hence the speed of train is (25y²  + 5y + 1) km/h.