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Renan found the sum (4.2x + 3) + (5.7x – 2) + (5 – 2.6x), as shown.

4.2x + 3 + 5.7x – 2 + 5 – 2.6x

4.2x + 5.7x + 2.6x + 3 – 2 + 5

(4.2 + 5.7 + 2.6)x + 3 – 2 + 5

12.5x + 6

What was Renan’s error in adding the expressions?
He used the commutative property incorrectly.
He used the distributive property incorrectly.
He added incorrectly.
He multiplied incorrectly.

1 answer

Renan's error in adding the expressions is that he added incorrectly.

To clarify, let's go through the calculation:

  1. The original expression is \( (4.2x + 3) + (5.7x - 2) + (5 - 2.6x) \).

  2. Combining like terms for \(x\):

    • \(4.2x + 5.7x - 2.6x = 4.2 + 5.7 - 2.6 = 7.3x\).

  3. Combining constant terms:

    • \(3 - 2 + 5 = 6\).

Thus, the correct sum should be \( 7.3x + 6\), not \( 12.5x + 6\).

Hence, Renan made an error in the addition of the \(x\) terms.