Simple interest

Pens8675309

New member
Joined
Apr 13, 2021
Messages
4
Compare the number of years it will take to double money at 5% interest, with simple interest and compounded annually. What is the difference in the number of years? (Round your answer to the nearest tenth , if necessary)
 

jonah2.0

Full Member
Joined
Apr 29, 2014
Messages
403
Beer soaked request follows.
Compare the number of years it will take to double money at 5% interest, with simple interest and compounded annually. What is the difference in the number of years? (Round your answer to the nearest tenth , if necessary)
Please show us what you have tried and exactly where you are stuck.

Please follow the rules of posting in this forum, as enunciated at:


Please share your work/thoughts about this problem.
 

skeeter

Elite Member
Joined
Dec 15, 2005
Messages
2,944

HallsofIvy

Elite Member
Joined
Jan 27, 2012
Messages
7,532
If A is the initial amount invested at 5% per year simple interest, the first year it earns 0.5A interest, the second year it earns 0,5A, etc., That is every year the account earns 0.5A interest so in n years the interest earned will be 0.5nA. In order that the account have doubled the interest earned must be equal to the amount originally in the account: 0.5nA= A. Solve that for n.

With interest compounded annually, the first year it earns 0.5A interest but that interest is add to the account so the interest the second year is 0.5(A+ 0.5A)= 0.5A+ 0.5^2A= A(0.5+0.5^2). The third year the interest earned is 0.5(A+A(0.5+ 0.5^2)= A(0.5+ 0.5+0.5^2+ 0.5^3). The nth year it would be A(0.5+ 0.5^2+ 0.5^3+ ...+ 0.5^n). Including the initial amount in the account, A, that is A(1+0.5+0.5^2+ 0.5^3+ ... + 0.5^n). That sum is a "geometric sum", a sum of the for a+ ar+ ar^2+....+ar^n for some a and r. Here a= 1 and r= 0.5.

Whoever gave you this problem clearly expects you to know how to sum a geometric series. If you don't, or if you need a review, look at Finite Geometric Sum - Bing images .
 
Last edited:
Top