The sum of the digits of a 2-digit number is 9. If the digits are interchanged, the new number is 45 less than the original. Find the number.
A63
B72
C81
D90
Explanation
Original number 10x + y. x+y=9. New number 10y + x. (10x+y) – (10y+x) = 45 => 9(x-y)=45 => x-y=5. x+y=9, x-y=5 => x=7, y=2. Number is 72.
Exam Relevance
- Topic: Number System
- Subtopic: Digit Problems
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