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Missing Second Number
When the second number is missing (5+__=9), you can count up from 5 to 9: 6, 7, 8, 9 — that is 4 counts. So the missing number is 4. Or you can subtract: 9-5=4. Both methods give the same answer!
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Mathematics — Missing Numbers: Finding the Unknown
When the second number is missing (5+__=9), you can count up from 5 to 9: 6, 7, 8, 9 — that is 4 counts. So the missing number is 4. Or you can subtract: 9-5=4. Both methods give the same answer!