Question

Two students determined the value of this expression.

Answer 1

Let's solve

$\\ \rm\rightarrowtail -2.5(1.4+3.1)+6.9(-4.3)$

$\\ \rm\rightarrowtail -3.5-7.75-29.67$

$\\ \rm\rightarrowtail -11.25-29.67$

$\\ \rm\rightarrowtail -40.92$

Both did error in signs

Answer 2

Answer:

Given expression:

-2.5(1.4+3.1) + 6.9(-4.3)

Student P

Step 1:  -3.5 + 7.75 + 6.9(-4.3)

Step 2: -3.5 + 7.75 - 29.67

Step 3: 7.75 - 3.5 - 29.67

Step 4: -25.42

Student P made an error in step 1.  When expanding the first part of the expression, they forgot the negative sign when multiplying -2.5 by 3.1.  

So Step 1 should be:  -3.5 - 7.75 + 6.9(-4.3).  

This error then impacted all following steps and gave an incorrect final solution.

Student Q

Step 1: -3.5 - 7.75 + 6.9(-4.3)

Step 2: -3.5 - 7.75 - 29.67

Step 3: -(3.5 - 7.75 - 29.67)

Step 4: -(-33.92)

Step 5: 33.92

Student Q made an error in step 3.  When placing the numbers in parentheses and placing a negative sign outside the parentheses, they should have changed the two negative signs inside the parentheses to positives.

So Step 3 should be: -(3.5 + 7.75 + 29.67).  

This error then impacted all following steps and gave an incorrect final solution.

Correct steps and solution

Step 1:  -3.5 - 7.75 + 6.9(-4.3)

Step 2: -3.5 - 7.75 - 29.67

Step 3: -(3.5 + 7.75 + 29.67)

Step 4: -(40.92)

Step 5: -40.92