Simple Interest.Help..(要式)

1. Karen deposits $ 9000 in a bank at 6% p.a. simple interest rate
for 2 years. At the same time, Jacky borrows $9000 from the
bank at 8.5% p.a. simple interest rate for 2 years.
( a ) How much interest will Karen earn?
( b ) How much interest will Jacky pay?
( c ) Find the net income that the bank will earn from Karen and
Jacky.
Sol:
( a )
9000 × 6% × 2
＝ 1080
( b )
9000 × 8.5% × 2
＝ 1530
( c )
1530 － 1080
＝ 450
Ans: ( a ) $1080 ( b ) $1530 ( c ) $450
2. How long does it take a sum of money to double itself if it earns
simple interest at an interest rate of 8% p.a.?
Sol:
1 ÷ 8%
＝ 1/0.08
＝ 12.5
Ans: 12.5 years
3. Wendy has a deposit in a bank. If the simple interest rate is
increased from 8% p.a. to 9.5% p.a., she will get an additional
interest of $62.5 every month. Find the deposit.
Sol:
9.5% － 8%
＝ 1.5% ...... increased interest rate
62.5 * 12 ÷ 1.5%
＝ 750/0.015
＝ 50000
Ans: $50000
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1a) Karen can earn:
$9000*6%*2
=$1080
b)Jacky will pay:
$9000*8.5%*2
=$1530
c)net income:
$1530-$1080
=$450