天山 04-21

[schung0529]

Martin has worked for the last 30 years. If his average(arithmetic mean) total annual earning for the first 5 year is $15000, what is his average total annual earnings for the last 5 years?

1) Martin's average total annual earnings for the first 25 year is $27000

2) Martin's average total annual earnings for the last 25 years is #34000


答案C, 請幫幫我吧

[waleaaa]

條件(1).(2)單獨來看　皆不充分
如果兩者同時成立時來看
由題目及條件(2)可得知30年共賺 15,000 * 5 + 34,000 * 25 = X
再由條件(1)可推算出答案為 [X - (27,000 * 25)] / 5
所以選C