Arithmetic · real student question

Evaluate 5 − [−2 + 5] − (−3) + 2.

Question

Evaluate

5[2+5](3)+25 - [-2 + 5] - (-3) + 2

Step-by-step solution

  1. Do the grouping symbols first. The order of operations settles brackets before any addition or subtraction outside them:

    2+5=3-2 + 5 = 3

    53(3)+2\Longrightarrow \quad 5 - 3 - (-3) + 2

    Note the sign in front of the bracket stays attached to the result, so it becomes 3-3, not +3+3.

  2. Rewrite the subtraction of a negative as addition. Because (a)=+a-(-a) = +a,

    (3)=+3-(-3) = +3

    53+3+2\Longrightarrow \quad 5 - 3 + 3 + 2

    This is the step most answers get wrong: the two minus signs cancel, they do not reinforce.

  3. Evaluate left to right. Addition and subtraction have equal precedence, so work strictly left to right:

    53=2,2+3=5,5+2=75 - 3 = 2, \qquad 2 + 3 = 5, \qquad 5 + 2 = 7

  4. Cross-check by grouping the signed terms. Collecting positives and negatives separately gives the same answer:

    (5+3+2)3=103=7(5 + 3 + 2) - 3 = 10 - 3 = 7

    The agreement of the two routes is a genuine check, because a mis-handled sign would break one of them.

  5. State the result.

    5[2+5](3)+2=75 - [-2 + 5] - (-3) + 2 = 7

    If the bracket had been read as +[2+5]+[-2+5] the answer would have been 1313, which is why the leading minus deserves the extra attention.

Answer

77

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