Question

The sum of the digits of a two - digit number is 15. if the the digits were reversed , the number increases by 9 . Find the number .

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Answer 1

Explanation:

no. 10y+x

no. formed by reversing the digits = 10x+ y

ATQ

EQ(1)= x+y=15

EQ (2)=10x+y+9=10y +x ( Digits are reversed)

9x-9y=-9

x-y=-1

x+y=15 ( given)

2x=14,x=7

and y=15–7=8

thus the number=78

Answer 2

78

Explanation:

Let the two-digit number have the digits a and b.

It mentions that they add up to 15.

Then the possible numbers are :

• 69 (6 + 9 = 15)
• 78 (7 + 8 = 15)

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Let's reverse the numbers :

69

• 69 ⇔ 96
• 96 - 69 = 27
• Not the right number ×

78

• 78 ⇔ 87
• 87 - 78 = 9
• This is correct √

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Solution :

Hence, the number needed is 78