Question

Shampoo is sold in two sizes.
The family size costs £3.48 and contains 270ml.
The regular size costs £1.99 and contains 160ml.
Which size is better value for money?

Answer 1

Hint: Here we have to compare the things. We can either compare the quantity or can compare money value. But for that they should be in the same quantity or same money value. i.e. either rate of 10ml for both or quantity we will get in £1.

Complete step-by-step answer:
We will compare with the quantity.
For family size,
270ml is for £3.48. We have to find the cost of 10ml. So we will use a unitary method.
Cost of 10ml is,
\[
   = \dfrac{{10 \times 3.48}}{{270}} \\
   \Rightarrow \dfrac{{34.8}}{{270}} \\
   \Rightarrow 0.128 \\
\]
For family size cost of 10ml shampoo is £0.128
For regular size,
160ml is for £1.99. We have to find the cost of 10ml. So we will use a unitary method.
Cost of 10ml is,
\[
   = \dfrac{{10 \times 1.99}}{{160}} \\
   \Rightarrow \dfrac{{19.9}}{{160}} \\
   \Rightarrow 0.124 \\
\]
For family size cost of 10ml shampoo is £0.124
Thus we are getting 10ml shampoo in £0.124 for regular size. So, regular size is better value for money.

Note: Here students can compare the quantities directly that will not lead to the correct solution. Because when we compare two objects they should be of the same quantity. It can be in terms of rate or quantity.