Question

the sum of two digit number is 7 when the digital reverse the number is decreased by 9 find the number

Answer 1

Let the ones digit be x,
and the tens digit be y

Then the number is 10y + x

And, according to question

=>x + y = 7 ..............(1)

Also, by reversing the digit of a two digit number, we get

=>10x + y = 10y + x -9
=>10x - x + y - 10y + 9 = 0
=>9x - 9y + 9 = 0
=>9(x - y + 1) = 0
=>x - y = -1 ..................(2)

Using equation 1 & 2 , we get
=>x + x + y - y = (7 - 1)
=>2x = 6
=>x = 3

Now from equation 2, we get
=>x - y = -1
=>3 - y = -1
=>y = 4

The two digit number is 10y + x
=>(10 * 4) + 3
=>43

Hence, the two digit number is 43.

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