NIACL Model Paper 2 with solutions for free online practice

Question : 18 of 100

Marks: +1, -0

The sum of digits of a two digit number is 15. If 9 be added to the number, then the digits are reversed. The number is

96
87
78
69
None of these

Solution:

(c) Let the two digit number be 10x + y
We have x+y= 15....... (i)
and(10x+y) + 9 = (10y+x) or 9x-9y = -9
or x-y = -l ...........(ii)
From (i) and (ii) x = 7 and y = 8
The number is

10×7 + 8 = 78

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