SSC CGL 2025 Tier-I · 17 September 2025, Shift 2 · Quantitative Aptitude · Question 6 of 99

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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SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

In a group of 40 boys, the average height was initially determined to be 160 cm. However, it was later discovered that the height of one boy was incorrectly recorded as 165 cm when it should have been 156 cm. Calculate the accurate average height.

(a)129.675cm
(b)150.845 cm
(c)159.775 cm
(d)179.275 cm

Answer

Why

Correct — C. Correct the total, then divide again.

Recorded total: 40 × 160 = 6400 cm
Excess in the wrong entry: 165 − 156 = 9 cm
Correct total: 6400 − 9 = 6391 cm

Correct average: 6391 ÷ 40 = 159.775 cm → option (c)

Shortcut: 160 − 9 ÷ 40 = 160 − 0.225 = 159.775 cm.

Why the others are wrong

(a)
129.675cm — 129.675 cm is about 30 cm below 160. Correcting one height by 9 cm lowers the 40-boy average by only 9 ÷ 40 = 0.225 cm.
(b)
150.845 cm — 150.845 cm is more than 9 cm below 160. The 9 cm error is shared across 40 boys, so the average falls by 0.225 cm, not by 9 cm or more.
(d)
179.275 cm — 179.275 cm is above 160, but the wrong entry overstated a height. Taking out the excess can only lower the average, to 159.775 cm.

Concept

A wrong entry distorts the total, and the average follows it. Rebuild the total from the recorded average, remove the error, and divide by the count again.

The average moves by the error shared across the group: 9 ÷ 40 = 0.225 cm. The wrong entry was too high, so the true average sits just below 160.

Three of the options sit 9 cm or more from 160 cm. A 9 cm error in one of 40 heights shifts the average by only 0.225 cm, so they fall at a glance.

Key facts

Correct total = recorded total − wrong value + right value.
Change in average = change in total ÷ number of items.
If a recorded value was too high, the true average is below the recorded one.

Study next

Corrections with two or more misrecorded valuesFinding the misread value when the corrected average is givenWeighted average of two groups of different sizes

Common traps

Adding the 9 cm instead of subtracting it, which gives 6409 ÷ 40 = 160.225 cm. The wrong entry was too high, so the total falls.
Taking the whole 9 cm off the average instead of 9 ÷ 40.

The same total-first method settles 24 Sep 2025, 16:00, Quant Q.13, where the top two of 12 results are dropped: 12 × 75 − 10 × 72 = 180, an average of 90 for the two.

Related PYQs

No directly related past PYQ was found.

Topic: Averages — all 76 SSC CGL questions on it, every solved shift.