Manoj crosses a 500 m long street in 5 minutes. What is his speed in km per hour?
- (a)5.5 km/h.
- (b)5 km/h.
- (c)6 km/h.
- (d)7 km/h.
Answer
Why
Correct — C.
Speed = distance ÷ time, then convert the units.
Divide by the minutes: 500 m ÷ 5 min = 100 m per minute
Multiply by 60 minutes: 100 × 60 = 6,000 m per hour
Divide by 1,000 m: 6,000 ÷ 1,000 = 6 km/h → option (c)
Why the others are wrong
- (a)5.5 km/h. — 5.5 km/h covers 5,500 × 5⁄60 ≈ 458 m in 5 minutes, about 42 m short of the 500 m street.
- (b)5 km/h. — 5 km/h covers 5,000 × 5⁄60 ≈ 417 m in 5 minutes, well short of the 500 m street.
- (d)7 km/h. — 7 km/h covers 7,000 × 5⁄60 ≈ 583 m in 5 minutes, which overshoots the 500 m street by about 83 m.
Concept
Speed = distance ÷ time, but only once both are in the units the answer asks for.
A quicker route here: 5 minutes is 1⁄12 of an hour and 500 m is 0.5 km. So speed = 0.5 ÷ 1⁄12 = 0.5 × 12 = 6 km/h.
Working per minute first and multiplying by 60 gives the same answer.
A handy conversion: 1 km/h = 1,000 m ÷ 60 min ≈ 16.67 m per minute, so 100 m per minute is 100 ÷ 16.67 ≈ 6 km/h.
Key facts
- 5 minutes = 5⁄60 = 1⁄12 hour
- 1 km/h = 5⁄18 m/s, and 1 m/s = 18⁄5 = 3.6 km/h
- 100 m per minute = 6 km/h
Study next
Common traps
- Dividing 500 by 5 and stopping at 100, which is m per minute, not km/h
- Multiplying by 60 but not dividing by 1,000, which leaves 6,000 m per hour
9 Sep 2024, 16:00, Quant Q.6 needs the same conversion the other way: a closing speed of 15 − 12 = 3 km/h is 50 m per minute, so a 600 m gap closes in the keyed 12 minutes.
12 Sep 2025, 09:00, Quant Q.19 turns 30 minutes into ½ hour: 240 × ½ = 120 km, plus 20% is 144 km, so the keyed new speed is 288 km/h.
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