Question

In the series12 15 21 the third trem is

Answer 1

in your series there may be 2 logic

1 - difference of 3, 6, 9, 12......

12+ (3) = 15

15+(6)= 21

21+(9)= 30

2- multiplication series of 3, 6, 12, 24, .....

12+(3)=15

15+(6)=21

21+(12)= 33

So, possible third term is 30 or 33

Answer 2

ANSWER

Let the tens digit of the required number be x and the units digit be y. Then,

x+y=12 .........(1)

Required Number = (10x+y).

Number obtained on reversing the digits = (10y+x).

Therefore,

(10y+x)−(10x+y)=18

9y−9x=18

y−x=2 ..........(2)

On adding (1) and (2), we get,

2y=14⟹y=7

Therefore,

x=5

Hence, the required number is 57.