The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg and that of B and C be 43 kg, then the weight of B is:

Given

• Avg(A, B, C) = 45 ⇒ A + B + C = 135
• Avg(A, B) = 40 ⇒ A + B = 80
• Avg(B, C) = 43 ⇒ B + C = 86

Goal: Find B

Step 1: Use totals
(A + B) + (B + C) = 80 + 86 = 166⇒ 2B + (A + C) = 166

Step 2: Replace (A + C)
A + C = (A + B + C) − B = 135 − BHence 2B + (135 − B) = 166⇒ B + 135 = 166 ⇒ B = 31 kg

Check

• A + B = 80 ⇒ A = 49; B + C = 86 ⇒ C = 55; then A + B + C = 135 ✓

Final Answer
Weight of B is 31 kg.