Final answer:
To simplify the expression 17/21 - (3/7 + 2/7), combine the fractions in the parentheses to get 5/7. Then, subtract 5/7 from 17/21 and simplify to get 2/21.
Step-by-step explanation:
To simplify the expression 17/21 - (3/7 + 2/7), we first find a common denominator for the fractions within the parentheses. Since both fractions have a denominator of 7, we can combine them as follows: (3/7 + 2/7) = 5/7. Now, we substitute this value back into the original expression:
17/21 - 5/7
To subtract fractions, we need a common denominator of 21. We can convert 5/7 into an equivalent fraction with a denominator of 21 by multiplying the numerator and denominator by 3:
17/21 - 5/7 = 17/21 - (5/7) * (3/3) = 17/21 - 15/21 = 2/21
Therefore, the simplified expression is 2/21, which corresponds to option D.