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To find out which number is missing, we solve the entire exercise to know which number we will have to add to obtain a result of 20:
To make 9 equal to 20 we will have to add the number 11.
Let's verify:
\( 8 - 2 + 6 = \)
Because there's another number in the equation! You have 7 + ? + 2 = 20, so you need to account for all the addends. First add the known numbers: 7 + 2 = 9, then subtract from 20.
You'll get the wrong answer! Always combine what you know first. Think of it like this: 'I have 7 and 2, that's 9 total. I need 20, so I'm missing 11.'
Substitute your answer back into the original equation. Replace the ? with your number and see if both sides equal 20. For example: 7 + 11 + 2 = 20 ✓
Yes! You can also think of it as . Subtract each known addend from the total: .
Same strategy! Add all the known numbers first, then subtract that sum from the total. The method works no matter how many addends you have.
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