Let A1, A2, A3, , A39 be 39 arithmetic means between the numbers 59 and 159. Then the mean of A25, A28, A31 and A36 is equal to :
- 129
- 136
- 131.50
- 134
Answer
(4) 134
Solution
59, A1, A2, , A39, 159 form an A.P. of 41 terms.
159=59+40d d= 52
Ak=59+kd=59+ 5k2
Mean = A25+A28+A31+A364=59+ 52 25+28+31+364
=59+ 52 30=59+75=134
Answer: (4)