What is the rate of interest p.c.p.a.? I. An amount doubles itself in 5 years on simple interest. II. Difference between the compound interest and the simple interest earned on a certain amount in 2 years is Rs. 400. III. Simple interest earned per annum is Rs. 2000

$I.\frac{P*R*5}{100}=P\iff R=20$

  $II.P1+\frac{R}{100}2-P-\frac{P*R*2}{100}=400=>pR2=4000000$

  $III.\frac{P*R*1}{100}=2000=>PR=200000$

  $\frac{PR2}{PR}=\frac{4000000}{200000}\iff R=20$

Thus I only or (II and III) give answer.

 Correct answer is (D)