A sum doubles in 5 years at simple interest. What is the annual rate?

✅ Answer: 20%

👍 Simple Explanation:

A sum doubles in 5 years at simple interest.

👉 That means:
Interest = Principal

Using formula:
$ SI = \frac{P \times R \times T}{100} $

Now,
$ P = \frac{P \times R \times 5}{100} $

Cancel $P$:

$ 1 = \frac{R \times 5}{100} $

$ R = \frac{100}{5} = 20% $

⚡ Shortcut:

If money doubles in $T$ years (SI), then
$ R = \frac{100}{T} $

👉 Here: $ R = \frac{100}{5} = 20% $