Q148
ArithmeticAverages & Ages
The arithmetic mean of the numbers 9, 12, 15, 18, 20, 22 is increased by 1 if 15 is replaced by
- a.16
- b.17
- c.19
- d.21
Answer: (D) 21
The original mean is $\dfrac{9+12+15+18+20+22}{6} = \dfrac{96}{6} = 16$. The new mean must be 17, so the new total is $17 \times 6 = 102$, an increase of $102-96=6$ over the original total — so 15 must be replaced by $15+6=21$.