Expert: Lynn Houston - 11/22/2008

Question
Robert is on a diet and can have 500 calories for lunch. A 3- ounce hamburger on whole wheat bread has 315 calories and 12 fluid ounces of soda has 145 calories. How many french fries can he eat if there are 10 calories in one french fry?

I'm not sure how to do this equation. I'm taking Algebra 1 and this is one of the problems that is similiar on a test I will be taking.

Answer
(500 - 315 - 145)/10 = 4

Algebra is logic, so think about this logically.  Although it doesn't say it, I assumed that he is going to eat the hamburger and drink the drink for lunch, so he's already used 460 of his 500 calories.  That only leaves 40 calories for fries.  40/10(calories per fry) = 4.

Since this is algebra, your teacher might be looking for you to use a variable in the equation, so your eq would be

315 + 145 + 10f = 500 (this is exactly the same eq as above in a different format)  In this case f = fries and you'd solve for f by "undoing" everything that has been done to to.  315 and 145 are added to it, so you would subtract each from both sides of the = sign.

315 -315 + 145 -145 + 10f = 500 - 315 - 145
10f = 40 (divide both sides by 10)

f=4