Question

· When 9 is subtracted from a two digit number, the number so formed is reverse of the origina
umber. Also, the average of the digits of the original number is 7.5. What is definitely the origina
number?
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Answer 1

Let the number be 10x + y

$\frac{x + y}{2} = 7.5$

$x + y = 15 \: \: \: \: \: .....(1)$

$10x + y - (10y + x) = 9$

$x - y = 1 \: \: \: \: \: ........(2)$

Adding both equation we get

2x = 16

X = 8

y = 7

Number is 87.