ISRO EC 2025 Q.87: solution and answer

ISRO 2025 · ECQ.87 · 1 mark · MCQ

Andre and Betty together weigh 150 pounds. Betty and Chris together 180 pounds. Andre, Chris and David together weigh 360 pounds. Altogether, the four of them weigh 450 pounds. How much does David weigh? (1 mark)

(A)
60 Pounds
(B)
90 Pounds
(C)
160 Pounds
(D)
210 Pounds

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Answer and solution

ANSWER

David weighs 210 pounds, which is option (d).

Official answer: DSource: ISRO's final answer key of 15 May 2026

Let the weights (in pounds) be $A, B, C, D$ for Andre, Betty, Chris and David. The conditions are $A + B = 150$ , $B + C = 180$ , $A + C + D = 360$ and $A + B + C + D = 450$ .
Subtract the third equation from the total: $(A + B + C + D) - (A + C + D) = 450 - 360$ , so $B = 90$ .
From $A + B = 150$ : $A = 150 - 90 = 60$ .
From $B + C = 180$ : $C = 180 - 90 = 90$ .
From $A + C + D = 360$ : $D = 360 - 60 - 90 = 210$ .
Check: $60 + 90 + 90 + 210 = 450$ , which equals the stated total, and $A + B = 150$ , $B + C = 180$ and $A + C + D = 360$ all hold.
David weighs $210$ pounds, option (d).

KEY IDEA

Subtract the sum of the people in a given group from the total to isolate the one who is left out, then back-substitute into the other equations.

WATCH OUT FOR

Adding the first two statements and trying to deal with Betty twice, or forgetting to subtract Andre's and Chris's weights both from 360, which gives a wrong value for David.

From the ISRO EC 2025 paper. Also Q.87 of the ISRO Scientist/Engineer Computer Science 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 5 ISRO Numerical questions, with notes

ISRO EC 2025 Q.87: solution and answer

Answer and solution

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