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The sum of the digits in a two-digit number is 16. If 18 is added to the number, the digits get interchanged. Find the original number.
1. 97
2. 88
3. 79
4. 69

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Correct Answer - Option 3 : 79

Given:

Sum of digits of number is 16

Concept used:

When digits of a number gets interchanged, the unit place becomes the tens place and vice versa

Calculation:

Let the original number be (10x + y)

Now, A/Q

⇒ 10x + y + 18 = 10y + x

⇒ 9y – 9x = 18

⇒ y – x = 2      ----(1)

And x + y = 16      ----(2)

Adding equation(1) and (2)

⇒ 2y = 18

⇒ y = 9

From equation (1)

⇒ x = 7

∴ The original number is 79

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