Liu Bolin

This link takes you to a wonderful picture.  [I am linking to it because I don’t own the copyright and don’t think I should reproduce it here directly.]  Look at it before you read on.

It is a photograph of a supermarket shelf in China. 

At first glance it is nothing particularly remarkable.  But then, when you look closer, you can see the outline of a person.  The artist, Liu Bolin, has had his clothes, hands, head and face painted to match his background, so he almost blends in, like a chameleon.

He has done this rather a lot in different situations, but this particular picture is my favourite because it can also be used to do some maths.

How I used it in class

As part of the starter activity I projected the picture while the pupils were arriving.  It was good to see how closely they were paying attention (the sudden “oh my goodness - there’s a man there”) was a giveaway!   

We then discussed what questions they would be able to answer.  They came up with:

·         How many bottles are there?

·         How many cans are there?

·         How much liquid is there?

·         How long would all this drink last one person?

·         What percentage of the shelf is covered by the man?

·         What fraction of the picture is taken up by the man?

I gave them a copy of this on paper (I fitted two copies of the image on one sheet and printed them out in black and white).  We decided there were two rows of bottles and assumed that there were also two rows of cans.

The question the pupils then worked on was: “how much weight are the shelves holding?”.

Some pupils wanted to know how much liquid each type of container holds.  Others explained that the large bottles on the bottom shelf were 2 litre bottles, the smaller ones looked like 500ml bottles and the cans hold 330ml. 

Someone pointed out that three cans stacked up could be treated as 1 litre (330ml x 3 = 990ml).  We also knew the answer wouldn’t be exact because we don’t know the weight of an empty bottle/can.

Finally, we needed to know how heavy the liquid is.  Someone knew that a litre of water has a mass of 1kg.  We decided that other drinks were likely to have a very similar density to that of water.

The generally agreed answer was just over half a tonne.

What did the pupils gain from doing this?

They used different conversions (and most learned that a litre of water has mass 1kg), including converting kg to tonnes.

They had to make decisions about what sorts of estimating they could and should do.

They had opportunities to decide on questions to work on (and did work on these after answering the question above).