# A Prime Number between 10 and 50 remains unchanged if its digits are reversed

A prime number between 10 and 50 remains unchanged if its digits are reversed. Then the square of such a number is

- 121
- 484
- 1089
- 1936

. **The value of X = 50**

__Solution-__

Formula of Average = (sum of observation/No. of observation)

Observations= 5, 10, 15 and X.

No. of observation= 4

Sum of observation = 5+10+15+X.

Average = 20 (Given)

(5+10+15+X)/4 = 20

(30 + x)/4 = 20

30+x = 20×4

X = 80 – 30

**X = 50 Ans.**