Christina B. answered • 03/21/19
Experienced, Positive, and Effective Tutor with an M.Ed.
Hi Karen,
You're correct that each piece will be 1/7 of the length of the original piece. But what is that length in meters?
Let's do a practice problem with a different length ribbon so that I don't give away the exact answer.
Susan cut a piece of 4 meter ribbon into 7 equal pieces. What is the total length of 5 of those pieces?
First we need to find out the length of one of the pieces. So, what is 4 meters divided by 7?
4÷7=4/7m
each piece of ribbon is 4/7m
So now we want to know what the total length of 5 of those pieces is. We can find that through addition, but multiplication is more efficient. Either method will give you the same answer, however.
4/7m × 5 or 4/7m+4/7m+4/7m+4/7m+4/7m
4/7m × 5 = 20/7 = 2-6/7m
The total length of five pieces of ribbon will be 2-6/7m.
You will follow the same steps to solve the original problem that you posted:
1) Divide to find the length of each piece of ribbon.
2) Multiply to find the total length of the pieces all together.
In math there are often multiple strategies for solving a problem, all of which will get you the same correct answer. Another way of thinking about this is that you are trying to find the length of 3 sevenths of the ribbon, or 3/7. The question is then "What is 3/7 of 1/2?" When you are working with fractions, "of" is a clue that you need to multiply. You could solve this problem by multiplying 3/7 × 1/2. From the way the problem is written, I think that you are expected to solve it in two steps. I did want to present both options, though, so you can think about what makes the most sense to you.
