求助另一道Prep!....

mop000

An investment of d dollars at k percent simple annual interest yields &600 interest over a 2-year period. In terms of d, what dollar amount invested at the same rate will yield $2,400 interest over a 3-year period?

答案是8d/3, 我心情激动算出4d/3.
怎么回事？！？！？

求助哪位高手指教！！！多谢！！！

cckjenius

SI = P*N*R /100
where p-principal n- number of years r-rate
SI- SIMPLE INTEREST

GIVEN:

600 = d * 2 * k/100
kd = 600*50 (1)

Lets say x is the principal we need to find in terms of d

2400 = x * 3 *k/100
x = 2400 *100/3k
= 2400 * 100 * d / 3 * 600 *50 (from (1) k = 600*50/d)

8d/3

mop000

讲得非常透彻！！！雪中送碳！！！不胜感激！！！
天呐！！加洲高中数学教育出来的后果就是我这样！！后悔没在国内读！！！
赶紧把您讲的公式背好！！