Mathematics

1.)Tom deposits $15000 in a bank for 5 years at an interest rate of 4% p.a. Keith deposits a different sum of money in the same bank for 10 years at an interest rate of 10% p. a. If the simple interests they receive are the same , how much does Keith deposit??
Tom 5 年所收的利息
15000 * 4% * 5 = $3000
Keith 存入 x 元，則10年可以收 3000元
x * 10 * 10% = 3000
x * 10 * 0.1 = 3000
x = 3000元
所以Keith deposit存入了3000元

Let $a be the money keith deposited.
$1500x4%x5=10ax10%
300=a
a=300
Keith deposited $300.