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## 6th grade

### Course: 6th grade > Unit 6

Lesson 7: Evaluating expressions word problems- Evaluating expressions with variables: temperature
- Evaluating expressions with variables word problems
- Evaluating expressions with variables word problems
- Evaluating expressions with variables: cubes
- Evaluating expressions with variables: exponents

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# Evaluating expressions with variables word problems

Learn to evaluate expressions in word problems to gain new information.

### Reflection question

# Let's try a practice problem!

# Challenge problem

### Extra challenge

Explain to a family member, friend, or classmate why the cost of six roses is

*not*double the cost of three roses.## Want to join the conversation?

- This extra challenge has frozen the two brain cells I had to rub together, and fried them at the same time, which I did not know was possible. There's simply not enough information to make an informed, rational decision. I mean, who's writing these challenges? 10 out of 10 for style... I think it has something to do with overhead costs and distance to travel, but I just can't sort it out with any clarity.(50 votes)
- The expression 2 + 5r for the total cost of r roses means $5 per rose plus a constant $2 fee for the entire purchase. If the number of roses is doubled (for example, 6 roses instead of 3 roses), only the cost of the roses without the fee is doubled, but the $2 fee is not doubled to $4. So doubling the number of roses comes $2 short of doubling the total cost.

Algebraically, the total cost of 2r roses is 2 + 5(2r) = 2 + 10r dollars.

However, twice the total cost of r roses would be 2(2 + 5r) = 2(2) + 2(5r) = 4 + 10r dollars.

So once again, we see that doubling the number of roses comes $2 short of doubling the total cost.

Have a blessed, wonderful day!(45 votes)

- how do you find the value of the muffins and cakes? it doesn't give enough info?(10 votes)
- It gives all the info you need.

We have the expression:**2m+10c**

Where**m**are muffins and**c**are cakes.

the question is :*How much money does the dessert store make from selling***three**muffins and**four**cakes?

So**m**= 3 and**c**= 4

Now just plug muffins and cakes into the expression**2m+10c**

2(3) + 10(4) or 2*3+10*4, both are the same thing

Now do the multiplication first and it becomes:

6 + 40

= 46

$46 dollars for 3 muffins and 4 cakes(21 votes)

- the extra challenge is making me loose my brain cells(14 votes)
- gurl its not that hard(2 votes)

- Cam has 32 dollars. How many roses can he afford to buy?

Assume that he wants to buy as many roses as he can. The answer is he can buy 6 roses for $32 but I do not understand why that is the answer.(3 votes)- If he buys 6 roses, the cost (from the formula in the problem) is 2 + 5r = 2 + 5(6) = 32.(10 votes)

- can you explain 100+20(51/4)(5 votes)
- 100+20(5 1/4)

Follow order of operations rules - PEMDAS:

You must multiply 1st.

-- Change 5 1/4 into an improper fraction = 21/4

-- Multiply: 20 (21/4) = 20/1 * 21/4 = 5 (21) = 105

Your expression is now: 100+105

Add the 2 numbers and you'll have your answer.(6 votes)

- What does it mean mathematically if you "plug something in"?(2 votes)
- It's called "substitution". You replace one item with another of equal value.(9 votes)

- What does the 2 signify in the equation 2+5r?(4 votes)
- Here 2 is just 2! It's a constant, which means that it doesn't change. 5r can change depending on what r is. So, if we let r = 4, then 2+5r becomes 2+5(4), which becomes 2+20= 22. If r had been a different number we would get a different answer. But 2 is always going to get added to 5r, regardless of what r is. Hope this helps.(3 votes)

- what do I do on the extra challenge?(4 votes)
- Follow the instructions. Explain why 2+5r is NOT equal to double of the cost of 3 roses.(3 votes)

- I have no idea how to do this. Can someone explain what he did in the video?(5 votes)
- I do not understand the second one the problem(5 votes)