Number System Ques 18
Question
When 9 is subtracted from a two digit number, the number so formed is reverse of the original number. Also, the average of the digits of the original number is 7.5. What is definitely the original number?
(1) 87
(2) 92
(3) 90
(4) 69
(5) 96
(IBPS Specialist Officer CWE (Prelim Exam) 31.01.2019)
Show Answer
Answer: (1)
Solution: (1)
Let the original number be $10 x+y$.
On subtracting 9,
$10 x+y-9=10 y+x$
$\Rightarrow 10 x+y-10 y-x=9$
$\Rightarrow 9 x-9 y=9$
$\Rightarrow x-y=1$… (i)
Again, $x+y=2 \times 7.5$ $=15 \ldots$. (ii)
On adding,
$2 x=16 \Rightarrow x=8$
From equation (ii),
$8+y=15 \Rightarrow y=15-8=7$
$\therefore$ Number $=8 \times 10+7=87$
BETA
