SSC CGL 2024 Tier-I · 12 September 2024, Shift 3 · Quantitative Aptitude · Question 11 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.

Two pipes A and B can fill a tank in 1 1⁄3 hours and 2 hours, respectively. If both the pipes are opened simultaneously, then in

Answer

Why

Correct — C. Turn each filling time into a rate, add the rates, then invert.

A takes 1⅓ hours = 4⁄3 h, so A fills 3⁄4 of the tank per hour
B takes 2 hours, so B fills 1⁄2 of the tank per hour
Together: 3⁄4 + 1⁄2 = 5⁄4 tank per hour

Time = 1 ÷ 5⁄4 = 4⁄5 hour
4⁄5 × 60 = 48 minutes → option (c)

Why the others are wrong

(a)
Option (a) reads 1¼ hours, which is 5⁄4 written as a time. But 5⁄4 is the combined rate in tanks per hour; the time is its reciprocal, 4⁄5 hour.
(b)
Option (b) reads 55 minutes. For the pair to take 55 minutes, B would have to fill the tank in about 2 hours 56 minutes, not the 2 hours the question states.
(d)
Option (d) reads 1⅔ hours, which is the plain average of the two times, (4⁄3 + 2) ÷ 2. Work problems add rates, never average times — and 1⅔ hours is slower than pipe A alone.

Concept

Pipes and cisterns is work-and-time under another name. A pipe that fills a tank in t hours does 1⁄t of the job per hour, and pipes running together simply add their rates.

The conversion that decides most of these questions is the mixed number: 1⅓ hours is 4⁄3 hours, so the rate is 3⁄4 per hour. Working from a decimal 1.33 instead loses the exactness the options are printed in.

Only after the combined rate is a single fraction do you invert it, and only then convert to minutes.

This question is stored in the response sheet as an image, and the captured line stops at then in, so the words naming what is asked are not visible. The keyed value, 48 minutes, is exactly the time for the tank to fill completely, which fixes the reading.

Key facts

A pipe that fills a tank in t hours works at a rate of 1⁄t tanks per hour.
1⅓ hours is 4⁄3 hours, and the matching rate is 3⁄4 of a tank per hour.
A combined rate of 5⁄4 tanks per hour inverts to 4⁄5 of an hour, which is 48 minutes.

Study next

Tanks with an outlet pipe, where the emptying rate is subtractedTwo or more people finishing a job together, the same rate addition in wordsConverting fractional hours to minutes without rounding

Common traps

Adding the two times instead of the two rates.
Averaging the times, which produces 1⅔ hours.
Leaving the answer as 4⁄5 hour when every option is given in mixed hours or in minutes.

Rate addition is the whole of pipes and cisterns, and SSC dresses it as pipes, taps or two people painting a wall. The difficulty here is put in the mixed number 1⅓ hours rather than in the method.

Related PYQs

No directly related past PYQ was found.