a two-digit number is twice the sum of its digit. If the tens digit is 7 less than the unit digit, find the number.
Let x= the unit digit
Then y= the tens digit
And 10y+x= the number
x+y= the sum of the digits
Now we are told that 10y+x=2(x+y) ------1st equation
We are also told that y=x-7 ----------- 2nd Equation
So our equations to solve are:
(1) 10y+x=2(x+y)
(2) y=x-7
Hope it helps