Porridge
To make porridge, Goldilocks mixes oats and wheat bran..... what percentage of the mix is wheat?
Age
14 to 16
Challenge level
Problem
To make porridge, Goldilocks mixes together 3 bags of oats with one bag containing 20% wheat bran and 80% oats. All the bags have the same volume. What percentage of the volume of Goldilocks' porridge mixture is wheat bran?
If you liked this problem, here is an NRICH task that challenges you to use similar mathematical ideas.
Student Solutions
Answer: 5%
Using fractions
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20% is the same as $\frac15$
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$\dfrac{\frac15}4$ is the same as $\frac1{20}$
$\frac1{20}$ = 5%
Using percentages
4 bags 100% (total oats and wheat bran)
1 bag 25%
20% of 1 bag 20% of 25% (amount of wheat bran) = 5%
Using decimals
There are 3.8 bags of oats and 0.2 bags of wheat bran
0.2 bags out of 4 bags is the proportion that is wheat bran
0.2 $\div$ 4 $\times$ 100 = 5%