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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 25:
To make 12 equal to 25 we will have to add the number 13.
Let's verify:
\( 3+2-1= \)
Adding the known numbers first (9 + 3 = 12) makes it easier to see what's missing. Then you can think: what number plus 12 equals 25? This approach reduces errors.
Yes, but it's not efficient! Systematic subtraction gives you the answer immediately. Save guessing for when you're stuck on harder problems.
The method stays the same! Whether it's or , always add the known numbers first, then subtract from the total.
Substitute your answer back into the original equation. Replace the ? with your answer: . If both sides are equal, you're right!
That's possible in some problems! If the total is smaller than the sum of known addends, you'll get a negative missing number. Always double-check your arithmetic.
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