The average weight of a group of 3 people A, B and C is 70 kg. When D joins this group, the average becomes 60 kg. One man E, whose weight is 5 kg more than of D , replaces A and the average weightog B , C, D and E now becomes 59 kg. A's weight ( in kg) is :
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 39
The average weight of A, B and C = 70 kg
⇒ The sum of the weight of (A + B + C) = 3 × 70 = 210 kg........(1)
The average weight of A, B, C, and D = 60 kg
⇒ The sum of the weight of (A + B + C + D) = 4 × 60 = 240 kg.......(2)
Weight of D =(weight of A, B, C and D) - (weight of A, B and C)
D = 240 - 210
⇒ D = 30 kg
Weight of E = Weight of D + 5
E = 30 + 5
⇒ E = 35
The average weight of B , C, D and E = 59 kg
(B + C + D + E)/4 = 59
⇒ (B + C + 30 + 35) = 236
⇒ B + C = 236 - 65
⇒ B + C = 171.......(3)
Eq (3) subtracted from eq (1)
⇒ (A + B + C) - B + C = 210 - 171
⇒ A = 39