At what rate percent per annum simple interest will a sum double itself in 10 years?
(a) 8%
(b) 10%
(c) 12%
(d) `12 1/2%`

Explanation

To find the rate percent per annum simple interest at which a sum will double itself in 10 years, we can follow these steps:

### Step-by-Step Solution:

1. **Define the Principal Amount (P)**:
- Let the principal amount be \( P \). For simplicity, we can assume \( P = 100 \) (this makes calculations easier).

2. **Calculate the Final Amount (A)**:
...