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Doubling
Objectives
To understand that doubling means multiplying by 2.
To work out efficient strategies for doubling two digit numbers using partitioning, and to be able to speed up doubling calculations, both written and mental.
Resources
Abacus 4 Textbook 1 | Squared paper
Today's Lesson
Times Tables
Remember to login to TT Rockstars to practise your times tables at least 5 times a week.
Main Activity
New students to the Wolsey Hall programme should learn the 9 times table, as well as doing the other mental warm ups.
Think up two different times and ask your student how much time there is in between them. Make sure there is
less than two hours difference; for example, tell your student a train leaves one station at 9.45 and arrives at another at 10.15. How many minutes did the journey take? At this stage, stick to multiples of 5, for ease.
Turn to page 49 in Abacus 4 Textbook 1.
Explain to your student that all the three digit numbers on the page are going to be doubled. Doubling is another way of saying ‘times 2’. However, no one knows their 2 times table so high. Therefore, it is necessary to partition the number into separate digits and to work with 1 or 2 digits at a time.
Watch the ‘Doubling’ video up to 3min 21 to understand how to double 3-digit numbers.
Once your student has understood the concept, ask them to double the numbers in Q3 – 12, but they should be set out like the example. Your student will find it easy to work with some 3 digit numbers, but others may need to be expanded, as in the first example. Allow your student to choose which method they feel most comfortable with.
Before attempting Q13, watch the video from 3:23 to understand how to double trickier numbers.
Watch out… Relying on doubling simply by doubling each digit in a number is a strategy that will only work when digits are 4 or less. This may cause difficulties when doubling numbers like 768: double 768 does not = 141216… Partitioning is the more error-proof method.