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IBPS RRB Officer Prelims 14 Nov 2016 Shift 1 Paper
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© examsnet.com
Question : 55
Total: 80
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 ?
87
92
90
69
96
Validate
Solution:
(1) Let the two-digit numberbe 10x + y,
According to the question,
10
x
+
y
–
9
=
10
y
+
x
⇒
10
x
+
y
–
10
y
–
x
=
9
⇒ 9x – 9y = 9
⇒ x – y = 1 .... (i)
and ,
x
+
y
2
=
7.5
⇒ x + y = 15 ... (ii)
On adding equations (i) and(ii),
2x = 16
⇒ x = 8
from equation (i),
8 – y = 1
⇒ y = 8 – 1 = 7
∴Required number
= 10 × 8 + 7 = 87
© examsnet.com
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