1. A sum of money doubles in 20 years on simple interest. It will get triple at the same

rate in:

a. 40 years

b. 50 years

c. 30 years

d. 60 years

e. 80 years

First find the interest rate of the sum of money doubles in 20 years

2p=p (1+rt)

2=1+rt. T=20 years

2=1+20r

Solve for r to get the simple interest rate

2-1=20r

20r=1

R=1:20

R=0.05

Now find how long will get triple at the same rate

3p=p (1+rt)

3=1+rt. R=0.05

3=1+0.05t

Solve for t

3-1=0.05t

0.05t=2

T=2:0.05

T=40 years ... answer