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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!(48 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(22 votes)

- the extra challenge is making me loose my brain cells(15 votes)
- gurl its not that hard(4 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"?(3 votes)
- It's called "substitution". You replace one item with another of equal value.(10 votes)

- I literally don't understand anything why is the first answer 10 and not 53 that makes no sense if I were to multiply 5 by ten that would be 50 and if I add 3 that would be 53 this makes no sense what so ever(3 votes)
- 1st Question: What is Sal finding when he uses t=10?

The problem tells you "t" is the number of tickets. And, it tells you that the expression calculates the cost of tickets. So, if Sal is using t=10, he is find the cost of 10 tickets. The question didn't ask you to find the cost. It asked you what the end result would represent.

Also, the last option (the number of tickets that you can buy for $53) assumes that you know the cost and you don't know the number of tickets. The tickets is the given value.

Hope this helps.(8 votes)

- What grade is everyone going into?

I'm 6th.(5 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)

- I can't explain the extra challenge. I just used the formula that they said to use.(3 votes)
- The explanation is that the cost of 6 roses is not the same as the double the cost of 3 roses because after you multiply 6 by 5 you also have to add an extra 2 because that will make it 7r. After adding the cot will change no matter what. So if they had only told us 5r and do not add 2 then it would be the double of 3, but they also said to add 2 which makes this different from 3.

Hope this helps :)(2 votes)