问一道数学题

gmatdd0417

A bank account earned 2% annual interest, compounded daily for as long as the balance was under $1,000, starting when the account was opened. Once the balance reached $1, 000,the account earned 2.5% annual interest, compounded daily until the account was closed. No deposits or withdrawals were made. Was the total amount of interest earned at the 2% rate greater than the total amount earned at the 2.5% rate?

(1)The account earned exactly $25 in interest at the 2.5% rate.

(2)The account was open for exactly three years.

这题我有题意理解的问题：

假设存入的本金是a，存了n天，当存款小于1000的时候

a*(1+2%/365)^n 是本金+利息，题干中说Once the balance reached $1, 000，存的这个钱是怎么保证正好到1000的，假如最后一天结算完后是1001呢？所以这样的话就影响计算2.5%的部分了。

我看解析的意思都是说2%存到正好1000，然后按2.5%计算，这样1+2确实可以比出大小。

顺便再问一下，闰年对这道题目有影响吗？

andrew22要奋斗

只是比较大小，又不需要计算具体数值，闰年不会有太大影响的