ISRO EC 2023 Q.88: solution and answer

ISRO 2023 · ECQ.88 · 1 mark · MCQ

Which one will replace the question mark?

ISRO EC 2023 question 88: Three X-shaped figures side by side. — Figure from the ISRO EC 2023 paper. It is part of the question.

(A)
45
(B)
8
(C)
38
(D)
48

Answer and solution

ANSWER

The missing number is $38$ , option (c).

Official answer: CSource: ISRO's revised and final answer key of 16 February 2024

Each X has four outer numbers and one centre number. Look for a rule that gives the centre from the outer four.
First X: $0 + 6 + 2 + 4 = 12$ , and the centre is $10 = 12 - 2$ .
Second X: $6 + 2 + 8 + 10 = 26$ , and the centre is $24 = 26 - 2$ .
Both figures follow the same rule: centre $=$ (sum of the four outer numbers) $- 2$ .
Third X: $4 + 14 + 10 + 12 = 40$ .
Centre $= 40 - 2 = 38$ .
So the missing number is $38$ , which is option (c). The values 45, 8 and 48 do not fit the rule.

KEY IDEA

In number-figure puzzles, test the simplest relation first: the sum of the outer numbers compared with the centre. Confirm that one rule fits every complete figure before applying it to the incomplete one.

WATCH OUT FOR

Trying products or pairwise sums of opposite corners and not checking that the rule works on both complete figures. Another slip is forgetting the constant $- 2$ and answering $40$ , which is not an option.

From the ISRO EC 2023 paper. Also Q.88 of the ISRO Scientist/Engineer Computer Science 2023 paper. Every question of this paper · The full paper (PDF, ISRO) · All 11 ISRO Reasoning questions, with notes

ISRO EC 2023 Q.88: solution and answer

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