Question

at a fast food restaurants 4 cheeseburgers and 5 small fries have a total of 2310 calories. 3 cheeseburgers and 2 small fries have a total of 1330 calories. how many calories does each item contain?

Answer 1

x=cheeseburgers and y=fries

4x+5y=2310
3x+2y=1330

In order to do the substitution, you need to get one equation to have a positive number and one to have a negative of the same number with the same variable. In this case, we need to multiply the first equation by 3 and the second by -4.

Then add the equations together. The 12x and -12x will cancel each other out and you solve for y.

12x+15y=6930
-12x-8y=-5320
----------------------
7y=1610
y=230

Now go to one of the original equations and plug that in and solve for x.

4x+5(230)=2310
4x+1150=2310
4x=1160
x=290

Cheeseburgers contain 290 calories and fries contain 230 calories.

Hope that helps.