Question

the sum of two digit no. is 15 .if 9 is added to it ,the digits are reversed find the number.....

Answer 1

let the no.s be x and y
x+y = 15
10x+y+9 = 10y+x
9x-9y = -9
dividing by 9
x-y=-1
from x+y=15 and x-y=-1
we get
          x = 7 and y = 8

Answer 2

Answer:

Required number 87

Step-by-step explanation:

Let Ten's place digit = x

units place digit =15-x

\* Given sum of two digit number 15 *\

The original number = 10x+(15-x)

= 10x+15-x

= 9x+15 ---(1)

If digits are reversed,

ten's place digit number = 15-x

Unit place digit = x

New number = 10(15-x)+x

= 150-10x+x

= 150-9x -----(2)

According to the problem given,

" if 9 is added to it ,the digits are reversed "

9x+15+9 = 150-9x

=> 9x+24=150-9x

=> 9x+9x=150-24

=> 18x=126

Divide each term by 18 , we get

=> x = 7

Therefore,

substitute x = 7 in equation (1), we get

Required number = 9x+15

= 9×7+15

= 63+15

= 78

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