Question

212x5 is a multiple of 3 and 11,find the value of x
pls

Answer 1

As 212x5 is a multiple of 3

So, by divisibility test of 3 sum of digits must be multiple of 3

⇒2+1+2+x+5=0,3,6,9,12,15,18

⇒ 10+x=0,3,6....

⇒ x=2,5,8,.....(i)

Since,

212x5 is multiple of 11

So, by divisibility test of 11 difference of alternative sum of digits must be multiple of 11

(2+2+5)−(1+x)=0,11,22,33

⇒ 8−x=0,11,22

⇒ x=8....(ii), all other numbers gave negative numbers.

From eq (i) and (ii), we have

x=8

So, number is $21285