Question

Jenny is working on simplifying the algebraic expression 3x+21
when x=5
. Her steps are as follows:

Step 1: 35+21

Step 2: 15+21

Step 3: 36

In which step did Jenny make a mistake? What should she have done differently?

(1 point)
Responses

Step 1, Jenny should've multiplied 3⋅5
instead of writing 5 as the exponent.
Step 1, Jenny should've multiplied 3 times 5 instead of writing 5 as the exponent.

Step 2, Jenny should've added 3 and 5 to get 8.
Step 2, Jenny should've added 3 and 5 to get 8.

Step 2, Jenny should've calculated the value of 35
to be 243.
Step 2, Jenny should've calculated the value of 3 to the 5th power to be 243.

Step 3, 15+21
should be 15⋅21
.
Step 3, 15 plus 21 should be 15 times 21.

Answer 1

The mistake in Jenny's steps is in **Step 1**. She incorrectly wrote "35 + 21."

When substituting \( x = 5 \) into the expression \( 3x + 21 \), she should have calculated it as follows:

1. **Substitute** \( x = 5 \) into \( 3x + 21 \):
\[
3(5) + 21
\]
2. **Calculate** \( 3(5) = 15 \):
\[
15 + 21
\]
3. **Add** \( 15 + 21 = 36 \).

So, Jenny should've multiplied \( 3 \times 5 \) instead of writing \( 35 \).

Thus, the correct response is:
**Step 1, Jenny should've multiplied 3 times 5 instead of writing 5 as the exponent.**