This equation is another order-of-operations challenge.
The expression is 21 − 7 ÷ 7. Division must be completed before subtraction, so calculate 7 ÷ 7 first.
7 ÷ 7 = 1. The expression then becomes 21 − 1.
Answer: 20.
A common mistake is subtracting 7 from 21 first. But under the standard rules of arithmetic, division comes before subtraction. Once that first step is handled correctly, the rest is easy.
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