Simple Interest.. just 5 questions.. i promise =)?

Can you do these for me? and please show working out..


if i get working out shown then i can understand my OTHER questions..


i know the formula but im just confused in this..








1) Find the simple interest rate for a sum to three times itself in 10 years time.





2) In how many years will a sum of money double itself at 12%p.a. simple interest?





3) Jane puts $2500 on August 4, 1981 in a saving bank. If the rate of simple interest is 12.5% p.a. What will be the amount on June 28, 1983??





4) Divide $5000 into 2 parts such that the simple interest on one part at 10% for 3 years, should be equal to that on the other at 12% for 2 years.





last one..





5) $100 000 is put on 28th of April in a 6 month fixed deposit account at 5% p.a and is withdrawn on 8th December in the same year. Find the total interest obtained, the overdue interest being calculated on daily basis and at 3.5% p.a.





Thanks so much.. please show working out so i know how to do the other similar questions.|||1)


Let the amount of principle be p, then the total amount at the end of 10 years is 3p. Thus the interest earned in 10 years is 3p - p = 2p.





Substituting I = 2p, P = p and T = 10 into the interest formula I = PRT, we have





2p = pR*10





Solving for R, we have


R = 2p/10p = 2/10 = 20%





2)


Let the amount invested be p, then the amount at the end is 2p. The total interest earned is 2p - p = p.





Substituting P = p, I = p and R = 12% into I = PRT, we have


p = p*12%*T





Solving for T, we have


T = p/(p*12%) = 1/(12%) = 100/12 = 8.33(years)





3) Note that T = 1.9 years approximately


I = PRT = 2500*12.5%*1.9 = 593.75


So the total amount of money on June 28, 1983 is 2500 + 593.75 = 3093.75|||I=PRT