Let x be the bigger number and let y be the smaller number.
x + y = 20
x = 2y -4
So now we substitute this value of x into the original equation.
2y - 4 + y = 20
3y - 4 = 20
3y = 24
y = 8
If y = 8, then
x = 12
because x + y must equal 20. To check this, let us see if these values work with the other equation
12 = (2*8) - 4
12 = 16 - 4
True -- so this is correct.
Assume that the numbers are x and y.
==> x+y=20....(1)
x=2y-4
Substitute with x=2y-4 in equation(1):
(2y-4)+y=20
3y-4 =20
ADD 4:
3y=24
Divide by 3:
y=24/3=8
==> x=2(8)-4 = 12
To check:\
12+8 = 20
12= 2(8)-4 =12