Three pencils cost 90c in the school shop.

What would one pencil cost? And how would you work out the price of seven?

Watch the four function machines. They show the two moves in turn: first divide to find what one costs, then multiply up to the amount we want. Watch for the divide step every time — that is where the price of one comes from.

We'll do these together on the machine, one problem at a time. An individual pupil comes to the board for each problem while the rest of the class follows and agrees. Each time, we key in a divide rule first to find the value of one, agree the answer as a class, then switch the same machine to a multiply rule to scale up.

• Six oranges cost €1.80. Find the price of one orange, then price ten.
• Five buns cost €2.00. Find the price of one bun, then price eight.
• A car goes 30 km in 3 hours at a steady speed. Find how far it goes in one hour, then how far in eight hours.

Each time it's the same two moves: divide to find one, then multiply up.

We'll work through these together at the board. Divide to find one, then multiply up:

• Nine buns cost €4.50. Find the price of one, then price four.
• A car goes 240 km in 3 hours at a steady speed. How far does it go in 7 hours?
• Six identical bottles hold 4.5 litres altogether. How much do ten bottles hold?
• Stretch: eight match tickets cost €60. How much do five cost?