Module 3 Calculating
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Can I extend my written methods for multiplying whole numbers to multiplying decimals by whole numbers?

Example review questions

  • Mike works out that 14 × 12 = 168. What is 14 × 1.2? How do you know?
  • Use a written method to calculate 24 × 13. What do you need to change to show a similar method to work out 2.4 × 13?
  • Use a written method to find the area of a swimming pool which is 25 m long and 7.5 m wide.
  • Complete the missing sections to work out 35 × 2.1:
    Blue square split into four sections. Top left shows a multiplication symbol. Top right shows a blank space and zero dot one. Bottom left has the number thirty with the number five below it. Bottom right has the number sixty with blank space to the right of it. Below this is a blank space with zero point five to the right of it.
  • Which is closer to 100: 5.2 × 17 or 7.2 × 15? Use written methods to prove your answer.

Teaching guidance

This teaching guidance document suggests some of the key vocabulary, models, images and practical equipment that children should experience and be able to use. It also includes some teaching tips to provide a few starting points for ways of supporting children with this area of mathematics.

PDF file Teaching guidance: Can I extend my written methods for multiplying whole numbers to multiplying decimals by whole numbers? | 42KB new window

Consolidation and practice

These resources are to support children in guided or independent work. Roll over the highlighted resource for a description.

PDF file How to use multiplication grid ITP | 145KB new window

SWF file Multiplication grid ITP | 26KB new window

XLS file Multiplication and division facts mixed
spreadsheet | 39KB new window

PDF file Problem-solving activity | 75KB new window

Visit the nrich website new window for further activities to support practice and application.

Multiplication grid

image alt text here

This interactive teaching program (ITP) is an ICT-based tool to support the exploration of multiplication. Multiplication grid ITP allows the child or teacher to demonstrate the grid method of multiplication for whole and decimal numbers. The ITP can be used to develop children's abilities to apply their knowledge of number facts and to deduce and reason, when finding missing component numbers.

Opportunities to use and apply

Possible contexts include:

  • Word problems, e.g. A can of drink contains 0.33 litres. How many litres are in 15 cans?
  • Area problems, e.g. Find the area of this shape:
    Blue square containing a purple shape with dimensions. The dimensions are eight point six meters across the top, nine point five metres on the right, eleven metres along the bottom and two meters on the left.
  • Gap calculations, e.g. Use a written multiplication to work out the missing number: empty box ÷ 3.8 = 17
  • Puzzles and problems, e.g. Organise the digits 9, 7, 5 and 3 into this calculation to give the greatest possible product
    empty box.empty boxempty box × empty box

Confirming learning

Ask probing questions such as:

  • Look at this example of a grid method. Complete the calculation and work out the answer.
    Grey box containing a blue grid with 6 squares, each square contains a question mark. At the top left hand corner of the grid there is a multiplication symbol. At the top of each square in the grid there are the numbers, from left to right, thirty, five and zero point two.
  • Abbie says that 23.4 × 5 will be bigger than 53.4 × 2. Is she correct? Use a written method to prove your answer.
  • I buy 1.6 kg of apples. They cost 65p per kg. Work out how much I will pay for the apples using a written method.
  • Work out the missing number: empty box ÷ 3.8 = 17