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Video: Solving Word Problems Involving Ratios

Tim Burnham

If 1 cup of rolled oats is used to make 37 oatmeal cookies, use the given ratio table to determine how many oatmeal cookies can be made with 5 cups of rolled oats.

01:57

Video Transcript

If one cup of rolled oats is used to make thirty-seven oatmeal cookies, use the given ratio table to determine how many oatmeal cookies can be made with five cups of rolled oats.

Now in this sort of problem, the number of cups of oats that we’ve got is proportional to the number of oatmeal cookies that we can make. And in fact we can see that for every one cup of oats, we can make thirty-seven oatmeal cookies. So the ratio of cups to cookies- and that means that how many cups of oats we’ve got we can make thirty-seven times that number of cookies.

Now in our problem, we’ve got five cups of oats. So we want to know how many oatmeal cookies we can make. Now if we started off with one cup, we can see from the ratio table that we’ve got five times as many cups. And with five times as many cups of rolled oats, we can make five times as many cookies. So to work out how many cookies we can make, it’s thirty-seven times five. Now thirty-seven times five is the same as thirty plus seven times five.

And we can use the distributive property of multiplication to present that as thirty times five plus seven times five. Now these calculations are a little bit easier to do in our head. Thirty times five is a hundred and fifty and seven times five is thirty-five. So we’ve got a hundred and fifty plus thirty-five which is one hundred and eighty-five. So five cups of rolled oats will enable us to make one hundred and eighty-five cookies.

Now another way of reading that table would be to say that one cup of oats makes thirty-seven oatmeal cookies. We’ve got five times as many cups of oats; so we’re going to be able to make five times as many cookies. Still comes up with the calculation thirty-seven times five, so we’ll still get the same answer.