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Which of these is equal to 18 times five?
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Hint: remember that you can replace one of the factors by an expression it is equal to.
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10 times eight times five, nine times nine times five, eight times two times five, nine times two times five.
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So which of these is equal to 18 times five.
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And the hint tells us that we can replace one of the factors by an expression it is equal to.
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The factors in this case are 18 and five.
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We have to replace one of the factors.
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It couldn’t be five because all of these expressions already have five in them.
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So it must be 18.
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So we need to replace 18 by an expression that it’s equal to.
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10 times eight is 80: that’s not equal to our factor 18.
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Nine times nine is 81: that’s not equal either.
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Eight times two is 16: so that’s not equal to 18 either.
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But nine times two is equal to 18.
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We can replace the factor 18 with the expression nine times two and then times that by five.
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So nine times two times five is equal to 18 times five.