Question

13. The sum of the digits of a two-digit number is 7. If 9 is added to the number, its digits are reversed. Find the number.
(Hint: Let units digit be x, then tens digit is 7 - x
The required number = 10(7 - x) + x = 70 - 10x + x = 70 - 9
The reversed number = 10x + 7 - x) = 9x + 7)
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Answer 1

Answer:

Let the units digit be y and tens place be x

the number will be (10x+y)

x+y=7

10x+y+9=10y+x

9x-9y=-9

x-y=-9

x+y=7

x-y=-9

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2x=-2

x= -1

y=7-x=7-(-1)=7+1=8