Respuesta :
Let the tens digit of the original number be represented by x. Let the ones digit be y.
The original number is then 10x + y, and the reversed number is 10y + x.
"Five times the sum of the digits is 13 less than the original number" becomes:
[tex]5(x+y)=10x+y-13[/tex]
"Four times the sum of its digits is 21 less than the reversed number" becomes:
[tex]4(x+y)=10y+x-21[/tex]
Work with the first equation until it is simpler:
[tex]5x+5y=10x+y-13 \\ 5x-4y=13[/tex]
Do the same thing with the second equation:
[tex]4x+4y=10y+x-21 \\ -3x+6y=21[/tex]
Now you have a system of two equations to solve.
[tex]5x-4y=13 \\ -3x+6y=21[/tex]
To eliminate x, multiply the first equation by 3 and multiply the second equation by 5
[tex]15x=12y=39 \\ -15x +30y=105[/tex]
Add the two equations.
[tex]18y=144 \\ y=8[/tex]
Aha! The one digit of the original number is 8. To find y, put x = 8 into any equation containing both x and y.
[tex]5x-4(8)=13 \\ 5x-32=13 \\ 5x=45 \\ x=9[/tex]
Sweet! The tens digit of the original number is 9. The original number is 98 and the reversed number is 89.
Their difference is 9.
The original number is then 10x + y, and the reversed number is 10y + x.
"Five times the sum of the digits is 13 less than the original number" becomes:
[tex]5(x+y)=10x+y-13[/tex]
"Four times the sum of its digits is 21 less than the reversed number" becomes:
[tex]4(x+y)=10y+x-21[/tex]
Work with the first equation until it is simpler:
[tex]5x+5y=10x+y-13 \\ 5x-4y=13[/tex]
Do the same thing with the second equation:
[tex]4x+4y=10y+x-21 \\ -3x+6y=21[/tex]
Now you have a system of two equations to solve.
[tex]5x-4y=13 \\ -3x+6y=21[/tex]
To eliminate x, multiply the first equation by 3 and multiply the second equation by 5
[tex]15x=12y=39 \\ -15x +30y=105[/tex]
Add the two equations.
[tex]18y=144 \\ y=8[/tex]
Aha! The one digit of the original number is 8. To find y, put x = 8 into any equation containing both x and y.
[tex]5x-4(8)=13 \\ 5x-32=13 \\ 5x=45 \\ x=9[/tex]
Sweet! The tens digit of the original number is 9. The original number is 98 and the reversed number is 89.
Their difference is 9.