Q. A number consists of two digits. The sum of the digits is 9. If 45 is subtracted from the number, its digits are interchanged. What is the number?
| (A) 63 | (B) 72 | (C) 81 | (D) 90 |
Ans: 72
Sol:
Let the two-digit number is AB The sum of digits = A + B = 9 If 45 is subtracted from the number, its digits are interchanged. ⇒ 10 A + B – 45 = 10 B + A ⇒ A – B = 5 ⇒ A = 7, B = 2 The required number = 72.
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