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Missing number problems
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Expressions involving an unknown number are needed to solve missing number problems. Unknown numbers are usually represented by letters.
x+10=12x + 10 = 12x+10=12
This is the same as asking: "what is added to 101010 to get 121212?"
The answer is x=2x=2x=2
Note: xxx is the letter commonly used for an unknown.
Anna has £20£20£20. She shares £5£5£5 with her brother and uses £12£12£12 to buy a new dress. how much money does she have left?
Write an expression:
5+12+x=205 + 12 + x = 205+12+x=20
Solve for xxx:
x=3x= 3x=3
Anna has £3‾\underline{£3}£3 remaining.
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Use trial and error to try out possible solutions.
Unknown numbers are usually represented by letters.
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