Question

One number is 4 plus one half of another number. Their sum is 31. Find the numbers.

Answer 1

13 & 18

Explanation:

Create the formulas:

0.5x+4=y

x+y=31

0.5x+4=y

Multiply both sides by 2

x+8=2y

x+y=31

Subtract 31 from both sides

x+y-31=0

Subtract y from both sides

x-31= -y

Multiply both sides by -1

-x+31=y

Multiply both sides by 2

-2x+62=2y

Combine equations:

-2x+62=x+8

Add 2x to both sides

62=3x+8

Subtract 8 from both sides

3x=54

Divide both sides by 3

x=18

0.5x+4=y

Subtract y from both sides

0.5x-y+4=0

Subtract 0.5x from both sides

-y+4= -0.5x

Multiply both sides by -1

y-4=0.5x

Multiply both sides by 2

2y-8=x

x+y=31

Subtract y from both sides

x= -y+31

Combine equations:

2y-8= -y+31

Add y to both sides

3y-8=31

Add 8 to both sides

3y=39

Divide both sides by 3

y=13

Answer 2

18, 13

Explanation:

x=4+1/2y

x+y=31

4+1/y+y=31

3/2y=27

y=18

x=31-18=13