The average of five positive numbers is 82.4. The average of the first two numbers is 66.5 and the average of last two numbers is 99. What is the third number?

 a) 81
 b) 82
 c) 83
 d) 84

SSC CHSL-2015

81. Solution The sum of the five numbers = 5 × 82.4 = 412 The sum of the first two numbers = 2 × 66.5 = 133 The sum of the last two numbers = 2 x 99 = 198 Then the sum of the four numbers = 133 + 198 = 331 So, the third number will be = 412 – 331 = 81