In a certain duration of time, a sum become 2 times itself at the rate of 5% per annum simple interest. What will be the rate of interest if the same sum becomes 5 times itself in the same duration?

20 Percent

Let Principal (P) = 1R

ATQ, 

                 Principal     :    Amount   :    S.I       :      Rate

i) Double:         1         :         2       :      1        :       5%

                                                            ⇓×4             ⇓×4

ii) 5 times:       1          :         5      :       4        :      20%