Why can't I just add 7 and 5?
Maya added -7 and 5 and got 12. She counted the sizes of both numbers but forgot that they move in opposite directions.
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3 lessons for “Adding signed numbers”
What does minus a negative really mean?
Diego saw 5 - (-3) and wrote 2, as if the problem were 5 - 3. But the two minus signs are doing different jobs.
Try this lessonWhat do two negatives in a row do?
Priya multiplied -3 by -4 and wrote -12. She remembered that negatives matter, but she got the rule backwards.
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Where did the negative sign go?
A negative sign belongs to the number next to it. Keeping that number together can prevent an almost-correct equation from turning into the wrong answer.
Try this lessonWhich pair of numbers factors x^2 + 7x + 12?
A trinomial like x^2 + 7x + 12 hides a pair of numbers. Find the pair, and the factored form falls into place.
Try this lessonWhy can't I add the x's to the plain numbers?
Lena simplified 5x + 3 + 2x + 4 and wrote 14x. She combined everything into x's, mixing apples with bananas.
Try this lessonWhy do exponents add when I multiply?
Rafi computed 2^3 * 2^2 by multiplying the exponents: 3 * 2 = 6, so he wrote 2^6 = 64. The exponents should add.
Try this lessonWhy can’t I add the denominators?
Before you add pieces, make sure they are the same size. The denominator names the pieces; the numerator counts how many you have.
Try this lessonWhy can't I just go left to right?
Jordan computed 3 + 4 * 5 by moving left to right: 3 + 4 = 7, then 7 * 5 = 35. The convention says multiply first.
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