SSC CGL 2024 Tier-I · 13 September 2024, Shift 2 · General Intelligence and Reasoning · Question 21 of 99

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 10 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.

What will come in place of the question mark (?) in the following equation, if ‘+’ and ‘–’ are interchanged and ‘×’ and ‘÷’ are interchanged? 107 + 2028 × 6 – 427 ÷ 7 = ?

(a)2785
(b)2758
(c)2578
(d)2268

Answer

Why

Correct — B. Rewrite the line under the interchange, then evaluate by BODMAS.

Rule: + and − trade places; × and ÷ trade places.

So 107 + 2028 × 6 − 427 ÷ 7 rewrites as 107 − 2028 ÷ 6 + 427 × 7.

2028 ÷ 6 = 338
427 × 7 = 2989
107 − 338 = −231
Then −231 + 2989 = 2758 → option (b)

Why the others are wrong

(a)
2785 — 2785 carries the right digits in the wrong order. The closing step is 2989 − 231, and that comes to 2758.
(c)
2578 — 2578 is another rearrangement of the same four digits. Re-do the last step on paper: 2989 − 231 = 2758.
(d)
2268 — 2268 is 490 below the true total. The two heavy steps fix everything else: 2028 ÷ 6 = 338 and 427 × 7 = 2989.

Concept

An interchange is gentler than a cycle: + and − swap with each other, × and ÷ swap with each other, so applying the rule twice restores the original line. Rewrite the expression in full, then run BODMAS on what you have written.

Order of operations matters more than the arithmetic here. Multiplication and division bind tighter than addition and subtraction, so 2028 ÷ 6 and 427 × 7 are both settled before anything is added.

The 107 is only combined at the end, and it is subtracted, not added.

Three of the four options are arrangements of the digits 2, 7, 5 and 8. A transposition while copying the answer down costs the mark even when every step of the arithmetic was right.

Key facts

Under the interchange, 107 + 2028 × 6 − 427 ÷ 7 becomes 107 − 2028 ÷ 6 + 427 × 7.
2028 ÷ 6 = 338 and 427 × 7 = 2989.
An interchange is its own inverse: swapping + and − twice returns the original expression.

Study next

Interchange items where numbers are swapped as well as symbolsBODMAS with a negative intermediate valueEquation-balancing items, where you pick the interchange that makes an equation true

Common traps

Working left to right after the rewrite.
Swapping one pair of symbols and leaving the other pair untouched, which gives −2544 here.
Copying 2758 down as 2785 or 2578.

Reasoning Q.17 of this paper sets the same task with a harder mapping — × to ÷, ÷ to +, and + to × — and rewards the same habit of rewriting the whole line before evaluating any of it.

Related PYQs

No directly related past PYQ was found.