Let us assume the unknown number to be = x
then
(33 1/3) * x = 21
(100/3) * x = 21
100x = 21 * 3
100x = 63
x = 63/100
= 0.63
So the unknown number in this question is 0.63. I hope the procedure is simple enough for you to understand. You can always use this procedure for solving similar type of problems in future without requiring any help from outside. I hope i have helped you in understanding this problem.
