Copyright © University of Cambridge. All rights reserved.

## 'How Big Are Classes 5, 6 and 7?' printed from http://nrich.maths.org/

Class 4 were making graphs. Ben, Ali, Katie and Charlene decided
to make graphs of the sizes of the seven classes in the school.

They went to the office to collect the numbers of children in
all the other classes. Ben and Ali wrote down the numbers for
Classes $1$, $2$ and $3$. Katie and Charlene wrote down the numbers
for Classes $5, 6$ and $7$. Of course they all knew the number of
children in Class $4$.

Ben and Ali drew a block graph. It looked like this:

Katie and Charlene decided to make theirs
differently. They drew this graph:

Miss Brown came along to look at their work.

"It's an interesting graph," she said, "but it's difficult to
tell how many children are in each class. Please can you make a
scale on it so we can all read it?"

Katie and Charlene did what they were told.

How many children were there altogether in Classes $5, 6$ and
$7$?