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Chris: This problem is all about decimals and fractions. A street artist likes to get people thinking.

So his latest work is a number puzzle within a pyramid.

In this pyramid, four of the bricks are marked with numbers, and a fifth contains a question mark.

The numbers on a particular brick can be found by adding the numbers on the two bricks underneath it.

So the sum of 0.8 and one half should be written on the pink brick.

What number should be on the brick marked with a question mark?

So why is this problem going to be hard?

Pupil: Because it's decimals and fractions.

Pupil: It's difficult to add decimals and fractions. Can you make this easier?

Pupil: You could try and draw it out and add the answers you know.

Pupil: You need to do this step by step so work your way up the pyramid and then back down.

Pupil: Give it a bash.

Did you work out the value of the brick with the question mark? Let's look at how we got our answer.

This problem involves decimals and fractions. It's probably easier if we convert the fractions into decimals first.

So if we change one half to 0.5, 0.5 plus 0.8 gives us 1.3 for the pink brick.

To find out the value of the brick with a question mark, we're going to have to work our way round it.

We can change 3/20 to 0.15 and add that with 0.8 to get 0.95.

If we add 0.95 and 1.3, we will get 2.25.

Now that we have one part of the value of the top brick, we can subtract this to find the value of the brick next to it.

So 3.4 subtract 2.25 means the other brick must be 1.15.

1.15 subtract 0.95 gives us 0.2.

And 0.2 subtract 0.15 gives us the final value of the brick with the question mark, it's 0.05

Great job solving this puzzle.