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Problem:

Chris made at least one error while finding the value of the following expression:
[tex]\[ 2(-20) + 3\left[\frac{5}{4}(-20)\right] + 5\left[\frac{2}{5}(50)\right] + 4(50) \][/tex]

Steps:

Step 1: [tex]\( 2(-20) + 3(-25) + 5(20) + 4(50) \)[/tex]

Step 2: [tex]\((3+2)(-20 + -25) + (5+4)(20 + 50) \)[/tex]

Step 3: [tex]\( 5(-45) + 9(70) \)[/tex]

Step 4: [tex]\( -225 + 630 \)[/tex]

Step 5: [tex]\( 405 \)[/tex]

Identify the step in which Chris made her first error. After identifying the step with the first error, write the corrected steps and find the final answer.

Response:

1. Identify the step with the first error:
- Step 1: [tex]\(2(-20) + 3(-25) + 5(20) + 4(50)\)[/tex]

2. Corrected Steps:
- Original Expression: [tex]\[ 2(-20) + 3\left[\frac{5}{4}(-20)\right] + 5\left[\frac{2}{5}(50)\right] + 4(50) \][/tex]
- Step 1: [tex]\( 2(-20) + 3(-25) + 5(20) + 4(50) \)[/tex] (Correct)
- [tex]\( \frac{5}{4}(-20) = -25 \)[/tex]
- [tex]\( \frac{2}{5}(50) = 20 \)[/tex]
- Step 2: [tex]\( -40 + (-75) + 100 + 200 \)[/tex]
- [tex]\( 2(-20) = -40 \)[/tex]
- [tex]\( 3(-25) = -75 \)[/tex]
- [tex]\( 5(20) = 100 \)[/tex]
- [tex]\( 4(50) = 200 \)[/tex]
- Step 3: [tex]\( -40 - 75 + 100 + 200 \)[/tex]
- Step 4: [tex]\( -115 + 300 \)[/tex]
- Step 5: [tex]\( 185 \)[/tex]

Final Answer: [tex]\( 185 \)[/tex]


Sagot :

Let's go through Chris's steps and identify where the first error occurred, then correct the steps and find the final answer.

### Chris's Steps Review:

1. Chris's Step 1: She begins with the expression:
[tex]\[ 2(-20) + 3\left[\frac{5}{4}(-20)\right] + 5\left[\frac{2}{5}(50)\right] + 4(50) \][/tex]
Evaluating each term:
[tex]\[ 2(-20) = -40 \][/tex]
[tex]\[ 3\left[\frac{5}{4}(-20)\right] = 3 \cdot (-25) = -75 \][/tex]
[tex]\[ 5\left[\frac{2}{5}(50)\right] = 5 \cdot 20 = 100 \][/tex]
[tex]\[ 4(50) = 200 \][/tex]
So Step 1 should be:
[tex]\[ -40 + (-75) + 100 + 200 \][/tex]
Chris did this step correctly.

2. Chris's Step 2: Combining terms incorrectly:
[tex]\[ (3 + 2)(-20 + (-25)) + (5 + 4)(20 + 50) \][/tex]
This is incorrect because she grouped and combined the terms incorrectly, changing the operations and not following the order of operations. Her mistake is here.

### Correct Steps:

Let's correct Chris's process:

Step 1: Evaluate each term separately:
[tex]\[ 2(-20) = -40 \][/tex]
[tex]\[ 3\left[\frac{5}{4}(-20)\right] = 3 \cdot (-25) = -75 \][/tex]
[tex]\[ 5\left[\frac{2}{5}(50)\right] = 5 \cdot 20 = 100 \][/tex]
[tex]\[ 4(50) = 200 \][/tex]

Step 2: Sum the evaluated terms:
[tex]\[ -40 + (-75) + 100 + 200 \][/tex]

Step 3: Perform the addition step-by-step:
[tex]\[ -40 + (-75) = -115 \][/tex]
[tex]\[ -115 + 100 = -15 \][/tex]
[tex]\[ -15 + 200 = 185 \][/tex]

The final answer is:
[tex]\[ 185 \][/tex]

So the final corrected answer for the expression [tex]\(2(-20) + 3\left[\frac{5}{4}(-20)\right] + 5\left[\frac{2}{5}(50)\right] + 4(50)\)[/tex] is [tex]\(185\)[/tex].