Correct Answer - Option 1 : 10%

Given:

Simple interest = 1/2(Principal)

Time (T) = 1/2(rate of interest)

Concept:

Simple interest is the interest calculated on the principal portion of the loan or the original contribution to the saving account.

Formula Used:

Simple Interest = (P × R × T)/100

Calculation:

Let the principal be '2P'

⇒ Simple interest = 1/2(2P) = P

Also, let the rate of interest be '2R'

So, time = (1/2)2R = R years

Simple Interest = (P × R × T)/100

⇒ P = (2P × 2R × R)/(100)

⇒ 100 = 4R^{2}

⇒ R^{2} = 100 ÷ 4 = 25

⇒ R = 5

So, rate percent per annum = 2R = 10%

∴ The rate percent per annum is 10%.