In a certain time, a sum becomes 4 times at the rate of

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In a certain time, a sum becomes 4 times at the rate of 5% per annum. At what rate of simple interest, the same sum becomes 8 times in the same duration ?

1. 12²/_{3 %}
2. 11³/_{5 %}
3. 11²/_{3 %}
4. 12³/_{5 %}

Correct Option: C

Let the sum be p
Then, for R = 5%
SI = (4p - p) = 3p
∴ 3p = (P x 5 x T)/100 = PT/20
⇒ T = 60 yr

Again, for another rate (R)
SI = (8P - P) = 7P
∴ 7P = (P x R x 60)/100
⇒ R = (7 x 100)/60 = 35/3%
= 11²/₃ %