How long is each piece? How many people can eat?

Question

1. A string length 3 1/2 m is divided into 5 equal parts. How long is each piece? 

 

2. Rosa bought 4/5 kg of dry lasagne. Each person needs 2/35. How many people can she feed?

Answer 1

Cyrill, both problems involve dividing by fractions.

 

For the first problem, the string is 3 1/2m long which must be divided into 5 equal sizes so the math would be 3 1/2 ÷5. To make the math easier, let's change the mixed number into an improper fraction, which would be 7/2 in this case so the problem is 7/2 ÷5. Because you are dividing a fraction, you need to make the second number "flip" to become a reciprocal and multiply it instead. The reciprocal of 5 is 1/5 (5/1 flipped is 1/5) so now the problem is 7/2•1/5. Multiplying all parts across, the answer is 7/10 so 7/10 m.

 

In the second problem, you have 4/5 kg that is broken up into 2/35 kg pieces to feed each person. The math is very similar, so you use the same method as before: 4/5 ÷ 2/35= 4/5 • 35/2 which is 140/10. This can simplified so now the answer is 14 people.