SSC CGL 2024 Tier-I · 12 September 2024, Shift 3 · Quantitative Aptitude · Question 13 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 6 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along with the current in 10 minutes. How long will it take to go 6 km in stationary water?

(a)1 hr 30 min
(b)1 hr 15 min
(c)2 hr 30 min
(d)1 hr 45 min

Answer

Why

Correct — A. Convert both legs to speeds first, then average them.

Upstream: 2 km in 1 hour → 2 km/h
Downstream: 1 km in 10 minutes = 1⁄6 hour → 1 ÷ 1⁄6 = 6 km/h

Speed in still water = (downstream + upstream) ÷ 2
= (6 + 2) ÷ 2 = 4 km/h

Time for 6 km = 6 ÷ 4 = 1.5 hours = 1 hr 30 min → option (a)

Why the others are wrong

(b)
1 hr 15 min — 1 hr 15 min means 6 ÷ 1.25 = 4.8 km/h in still water. The two legs are 2 km/h and 6 km/h, and their average is 4, not 4.8.
(c)
2 hr 30 min — 2 hr 30 min means 2.4 km/h, barely above the upstream speed. Still water is the midpoint of 2 and 6, which is 4 km/h, so the trip takes well under two hours.
(d)
1 hr 45 min — 1 hr 45 min is 1.75 hours, i.e. about 3.43 km/h — neither the average of the two legs nor either leg itself.

Concept

Boats and streams runs on two definitions: downstream speed = boat + current and upstream speed = boat − current.

Add the two and the current cancels, so the boat's own speed is the plain average of the two figures. Subtract them and the boat cancels, leaving twice the current — here (6 − 2) ÷ 2 = 2 km/h of stream.

Stationary water in the question means still water: the boat's own speed, with no current helping or resisting.

Neither leg is given as a speed. The 2 km and the 1 km are distances with times attached, so the conversion has to be done before any boats-and-streams formula can be used.

Key facts

Speed in still water is the average of the downstream and upstream speeds.
The current is half the difference between the downstream and upstream speeds.
Here the boat is 4 km/h and the stream 2 km/h, which reproduces the 6 km/h and 2 km/h legs.

Study next

Questions giving the ratio of downstream to upstream time instead of both speedsRound trips where the same distance is covered each wayConverting a leg timed in minutes into hours before dividing

Common traps

Using 10 as the time for the downstream leg without turning it into 1⁄6 hour.
Averaging the two times rather than the two speeds.
Marking the downstream or upstream speed because the 6 km distance matches 6 km/h.

SSC gives the two legs as distance-and-time rather than as speeds, so the first two lines of work are conversions and that is where the marks go. The still-water speed is then one average away.

Related PYQs

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