simple interest and compound interest

Question

Which of the following could be the no of complete years in which a sum of money put out at 20% yearly compound interest will become more than double but less than thrice?

 

(a)2

(b)3

(c)4

(d)5

(e)7

Answer 1

Some of your questions seemed to be poorly worded. If you deposit P dollars at 20 % simple interest. After 3 years you have

A = P*(1.2)^3 = 1.78P -- no this does not work

Try 3 years

A = P*(1.2)^4 = 2.07*P - so after 4 years you have 2.07 times the original amount. So the answer is 4 years.

 

I am available for online tutoring if you like.

Answer 2

Both c and d. c= 2.0736, d = 2.48832. the formula is (1+.2) ^ the number of years.