Write a system of equations for the situation. No need to solve!

Question

The sum of x and y is 25. When you subtract y from x you get 15. What are the two missing numbers.

I feel like the equations could be:

x + y = 25

y - x = 15

If someone could clarify if I'm right or wrong, that would be great! If wrong, please have an explanation! :)

Answer 1

Hi Eddie,

your first equation is great, but read carefully again the second part:

when you subtract y from x you get 15

if it helps, think of a quick, but unrelated example: If you subtract 1 from 16 you get 15, how would you write this? 16 - 1 = 15. NOT: 1 - 16 = 15 (Wrong!)

Answer 2

Hi Eddie,

In your problem you have 2 statements, so you can write 2 equations with 2 unknown variables.

1st statement : The sum of x and y is 25.

1st equation: x + y = 25

2nd statement: When you subtract y from x you get 15.

2nd equation: x - y = 15

To solve for x and y add both equations together.

x + y =25

x - y =15

-------------------------

2x = 40 ( y - y =0)

----------------------

2 x / 2 = 40 / 2 divide both sides by 2

x = 20

To find y substitute x value into equation 1 : x + y = 25

20 + y = 25 subtract 20 from both sides

y = 5

Hope this helps!