Math [Interest]
posted by Bob .
Okay, so I've been away from school for three weeks, and we have a math test tomorrow. I only just found out, and my friend emailed me the review questions. If someone could help me out, and show me how to do this, I'd appreciate it. No, I do not want someone to do my homework for me. I'm an idiot where math is concerned and I don't understand this.
1. Julie invests $500 at 5% simple interest. How long will it take to double in value?
2. Helen won the lotto when she was 18 and invested all the money at 4.5% compounding annually. When she was 24 it was worth $145073. How much did she win in the lotto?
3. Jessica has $150000 to invest for three years. She researches three investment options. Calculate the interest each option would earn and select the best option.
a. 5% pa simple interest
b. 4.5% pa compounding monthly
c. 4.25% pa compounding annually
4. Calculate the interest earned for the month in this cash management account.
Account Balance  Interest Rate
> $30000  3.5%
$30000$15000  2.95%
$15000$5001  2.5%
$5000$501  1.25%
$500 and under  0.5%
Date  Transaction  Balance
1 April  Opening Balance  $24903.25
15 April  Deposit $13500  $38403.25
23 April  Withdraw $30000  $8403.25

I'll try similar problems as the first two.
1. 10000 dollars at 4% interest would give 10000*4% = 10000*4/100=$400 per year.
To double, it would take 10000/400 = 25 years.
2. $1000 at 5% compound interest (compounded yearly) would give me in 5 years $1000*1.05^{5} = $1276.28.
If I received $4000 at the end of 5 years, I won (5 years ago, by proportions) $4000*(1000/1276.28)=$3134.10.
Give a try for #1 and #2 and the rest, and post what you've got. We'd be glad to help.