Question

The sum of the digits of a two digit number is 7. When the digits are reversed, then number is decreased by 9. Find the number

Answer 1

Let the first digit be a 
Let the second digit be b

The first condition

a+b=7 ...............................(1)

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The second condition

The first order value:
××a is a counting in tens. So actual value is 10×a
××b is counting in units. So actual value is 1×b

The first Order Value=10a+b...............................(2)
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The second order value:

××b is a counting in tens. So actual value is 10×b
××a is counting in units. So actual value is 1×a

The second Order Value=10b+a.........................(3)
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From the question
Equation (3)−Equation (2)=9.................................(4)

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Putting it all together

Equation 4 becomes→(10b+a)−(10a+b)=9

9b−9a=9..............................................(4a)
a+b=7...................................................(1)

From equation (1)
a=7−b

Substitute in (4a) giving:
9b−9(7−b)=9

9b+9b−63=9

18b=72

b=7218=4

Substitute in Equation (1) giving
a+b=7→a+4=7

a=3


Mark it brainlest

Answer 2

Hey mate,

x + y = 7--> x = 7-y

10y + x = 10 x + y - 9

Simplify:

9y = 9x - 9

9y = 9(7-y) -9

9y = 63 - 9y -9

18y = 54

y = 3

x = 4

The number is 43

hope this helps you out!