SSC CGL 2025 Tier-I · 23 September 2025, Shift 1 · Quantitative Aptitude · Question 3 of 100

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 13 September 2026.

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Dhanush crosses a road 100 metres wide in 50 seconds. His speed in km/hr is:

(a)9 km/h
(b)8.5 km/h
(c)8 km/h
(d)7.2 km/h

Answer

Why

Correct — D. Find the speed in m/s first, then convert to km/h.

Speed = distance ÷ time = 100 m ÷ 50 s = 2 m/s
1 m/s = 3,600 m per hour = 3.6 km/h = 18⁄5 km/h
Speed = 2 × 18⁄5 = 36⁄5 = 7.2 km/h → option (d)

Why the others are wrong

(a)
9 km/h — 9 km/h is 9 × 5⁄18 = 2.5 m/s. At that speed 100 m takes 40 seconds, not the 50 the stem gives.
(b)
8.5 km/h — 8.5 km/h is about 2.36 m/s, which covers 100 m in about 42.4 seconds. Dhanush takes 50 seconds, so he is slower than this.
(c)
8 km/h — 8 km/h is 8 × 5⁄18 ≈ 2.22 m/s, which crosses 100 m in 45 seconds. Dhanush takes 50, so his speed is lower.

Concept

Speed = distance ÷ time, and the units travel with the numbers. Metres ÷ seconds gives m/s, while the options are in km/h.

One hour has 3,600 seconds and one kilometre has 1,000 metres, so 1 m/s = 3,600⁄1,000 = 3.6 km/h, written 18⁄5.

Going the other way, multiply a km/h figure by 5⁄18 to get m/s.

Key facts

m/s to km/h: multiply by 18⁄5.
km/h to m/s: multiply by 5⁄18.
5 m/s = 18 km/h and 10 m/s = 36 km/h.

Study next

Train crossing a pole or a platform, where the distance is the train's lengthRelative speed of two bodies moving in the same or opposite directionsAverage speed over two legs at different speeds

Common traps

Multiplying by 5⁄18 instead of 18⁄5: 2 × 5⁄18 ≈ 0.56, smaller than the m/s value, which a km/h figure for the same speed never is.

The same cross-then-convert pattern appears at 21 Sep 2025, 16:00, Quant Q.5, where Manoj crosses a 500 m street in 5 minutes: 500 ÷ 300 = 5⁄3 m/s, and 5⁄3 × 18⁄5 = 6 km/h.

Related PYQs

No directly related past PYQ was found.

Topic: Time and distance — all 58 SSC CGL questions on it, every solved shift.