Number System Ques 10
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 RRBs Officer CWE (Pre.))
Show Answer
Answer: (1)
Solution: (1)
Let the two-digit number be $10 x+y$,
According to the question,
$10 x+y-9=10 y+x$
$\Rightarrow 10 x+y-10 y-x=9$
$\Rightarrow 9 x-9 y=9$
$\Rightarrow x-y=1$
and $\frac{x+y}{2}=7.5$
$\Rightarrow x+y=15$
On adding equations (i) and (ii),
$2 x=16$
$\Rightarrow x=8$
from equation (i),
$8-y=1$
$\Rightarrow y=8-1=7$
$\therefore$ Required number $=10 \times 8+7=87$
BETA
