A sum of money earns simple interest equal to 0.5 times the sum in 10 years; the rate of interest per annum is :

1. 20%

2. 10%

3. 5%

4. none of these

A sum of ₹ 600 put at 5% S.I. amounts to ₹ 720 in:

1. 3 years

2. 4 years

3. 5 years

4. 6 years

A sum of money, lent out at simple interest, doubles itself in 8 years. Find:

(i) the rate of interest.

(ii) in how many years will the sum become triple (three times) of itself at the same rate percent?