Doubles
To get a double of a number, we add the same number to itself. For example, double of 2 is 2 + 2 = 4.
Example: Michelle has 4 marbles and Jane has double the marbles that Michelle has. How many marbles does Jane have?
The double of 4 is 8.
So, Jane has 8 marbles with her.
It is easy to remember the numbers that we get by doubling one-digit numbers.
Doubles in addition:
The addition of any two consecutive numbers can be done by using doubles plus 1 or doubles minus 1 strategy.
Example: 2 + 3
The number 3 is one more than 2. So, we can write 3 as 2 + 1. So, the addition 2 + 3 can be shown as:
We already know the double of 2 is 4.
So, the required sum is one more than double. That is 5. Therefore, 2 + 3 = 5.
Example: 7 + 6
The number 6 is one less than 7. So, we can write 6 as 7 – 1. So, the addition 7 + 6 can be shown as:
We already know the double of 7 is 14.
So, the required sum is one less than double. That is 13. Therefore, 7 + 6 = 13.
Doubles plus 1 and doubles minus 1 are also called near doubles strategy.
This can also be extended to the numbers that are not immediately next to each other.
Example: 5 + 8
8 is 3 more than 5.
5 + 8 = (5 + 5) + 3 = 10 + 3 = 13
Doubles in subtraction:
An addend of an addition sentence will be the subtrahend/difference of the corresponding subtraction sentence.
We know that:
6 + 6 = 12
So, 12 – 6 = 6.
This can be pictorially shown as:
If you take away 6 from 12:
The remaining amount is 6.
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Fun Facts Since 2 + 3 is the same as 3 + 2, we can apply any of the near doubles strategies to find the sum. 2 + 3 = (2 + 2) + 1 = 4 + 1 = 5 OR 3 + 2 = (3 + 3 ) – 1 = 6 – 1 = 5 |
