Driving his car at the speed of 30 km/h Vinod reaches his office 5 min late. If his speed is 40 km/h, he reaches the office 3 min early. Find the distance he travels between his residence and his office.

Question

Question

This question was previously asked in

NTPC CBT-I (Held On: 4 Jan 2021 Shift 2)

Answer 1

Given:

Driving his car at the speed of 30 km/h Vinod reaches his office 5 min late and at speed of 40 km/h, he reaches the office 3 min early.

Concept used:

Time = Distance/Speed

Calculations:

Let the time be ‘t’ minutes to reach office

Let the distance be D.

Time for 30km/h

⇒ (t + 5)/60 = D/30 ----(1) (1 minute = 1/60 hours)

Time for 40 km/h

⇒ (t – 3)/60 = D/40 ----(2)

Subtract equation (2) from (1)

⇒ [t + 5 - (t - 3)]/60 = D/30 - D/40

⇒ (D/30) - (D/40) = 8/60

⇒ (4D - 3D)/120 = 8/60

⇒ D/120 = 8/60

⇒ D = 16 km

∴ The correct choice is option 1.

Shortcut Trick

Difference in time = Distance/Speed

⇒ [5 - (-3)]/60 = D/30 – D/40 (8 minutes = 8/60 in hours)

⇒ 8/60 = D/30 – D/40

⇒ D/120 = 8/60

∴ D = 16 km

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