Question

Two students determined the value of this expression.

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

These are the steps each student used.



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 - 29.6
Step 4: -25.42

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
Analyze the steps and describe any errors made by Student P and Student Q.

Answer 1

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

Answer 2

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