### When 21 is added to 30 % of a number, it gives the number itself. Find the number.

30

Step by Step Explanation:
1. Let us assume the number to be x.
30 % of x = x ×
 30 100
=
 30x 100

2. If we look at the question carefully, we will notice that the number(x) is equal to the sum of 21 and 30 % of x.
So, it can be written as:
x = 21 +
 30x 100

x =
 21 × 100 + 30x 100

x =
 2100 + 30x 100

By cross multiplying both the sides
100 x = 2100 + 30x
⇒ 100 x - 30x = 2100
⇒ 70x = 2100
x =
 2100 70

x = 30
3. Therefore, the number is 30.