RAS question
Find the missing number in the matrix (each row sums to 14): | 2 5 7 | | 3 4 7 | | 6 ? 7 |
Correct answer: (D) 1.
The missing number is 1 because the third row must satisfy 6 + 1 + 7 = 14.
Explanation
Each row in the matrix is governed by the same condition: its three entries must add up to 14. The first row confirms the pattern because 2 + 5 + 7 = 14, and the second row confirms it again because 3 + 4 + 7 = 14. The third row therefore has to obey the same sum. Since the known entries in that row are 6 and 7, they already contribute 13. The only number that completes the required row total is 1, because 6 + 1 + 7 = 14. The NCERT mathematics source supports this kind of step-by-step numerical deduction using sums, so the calculation directly identifies option D.
Why the other options are wrong
- (A) 5 would make the third row 6 + 5 + 7 = 18, which breaks the required row sum of 14.
- (B) 2 would make the third row 6 + 2 + 7 = 15, so the row would exceed the stated total by 1.
- (C) 3 would make the third row 6 + 3 + 7 = 16, which does not match the common row total.
Concept
This tests matrix-based number reasoning: identify the invariant across rows and use a simple missing-number equation. It recurs in RAS because mental-ability questions often reward spotting a compact arithmetic pattern rather than doing lengthy calculation.