Pies
Problem
Grandma had made pies for a bake sale. She had carefully put equal amounts of mixture in each pie tin and was now trying to find the weight of the pies.
She had a problem; she only had one $200$ gram weight and one $125$ gram weight.
She found that one pie balanced on the scale with both weights and a quarter of a pie.
How heavy was each pie?
Getting Started
What do the two weights weigh altogether?
If you took the quarter pie off the scales, what could you do to the whole pie to make the scales balance?
Student Solutions
Matthew and James recorded their answer as a fraction, 433 $\frac{1}{3}$ grams. Helena of Bebington and Christina, of Malborough Primary School, recorded their answers as decimal fractions. But each of these people used a combination of fractions and decimals to arrive at their solutions.
Can you follow their thinking as they calculated the answer?
Matthew explained the procedure he used:
I got my answer of 433 $\frac{1}{3}$ grams by putting the problem into an equation. These are the steps I took to get the answer:
- First I did the sum $200$g. + $125$g. which equalled $325$g.
- Then I wrote it down like this: $325$g. +
$\frac{1}{4}$ pie = pie
I then converted this to: $325$g. +$\frac{1}{4}$ pie = $\frac{4}{4}$ pie (or one whole pie). - Next, I took $\frac{1}{4}$ of a pie from each side leaving me with: $325$g. = $\frac{3}{4}$ pie.
- I multiplied each side by $4$ which came out as: $1300$ = $3$
pies
But Matthew only wanted to find the weight of one pie, so he did this last important step:
- I divided each side by $3$ and came to the final answer of:433 $\frac{1}{3}$ grams = $1$ pie."
Helena described her method this way:
$\frac{1}{4}$ pie = $325$g. divided by $3$, which is
$108.3$g.
So, $4 \times \frac{1}{4}$ of a pie = $4 \times108.3$g. or
$433.2$g.
$433.2$ grams is weight of a whole pie"
Teachers' Resources
Why do this problem?
Key questions
If you took the quarter pie off the scales, what could you do to the whole pie to make the scales balance?