The answer is: " 21 cookies ".
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Explanation:
To solve this problem:
We take the initial number of cookies: "99 cookies" (given); and subtract:
"78" cookies (given) from that number ; {that is; from "99" } ; to find the number of cookies that are left; as follows:
99 cookies
− 78 cookies
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21 cookies .
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That is: " (99 cookies) − (78 cookies) = " 21 cookies" .
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The answer is: " 21 cookies " .
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