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.

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!

the extra challenge is making me loose my brain cells

If the variable was multiplied by 5 only then it would double but then if you add 2 it won't double.

how do you find the value of the muffins and cakes? it doesn't give enough info?

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

can you explain 100+20(51/4)

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.

What does the 2 signify in the equation 2+5r?

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.

what do I do on the extra challenge?

Follow the instructions. Explain why 2+5r is NOT equal to double of the cost of 3 roses.

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.

If he buys 6 roses, the cost (from the formula in the problem) is 2 + 5r = 2 + 5(6) = 32.

What does it mean mathematically if you "plug something in"?

It's called "substitution". You replace one item with another of equal value.

Main content

6th grade

Course: 6th grade > Unit 6

Lesson 7: Evaluating expressions word problems

Evaluating expressions with variables word problems

Google Classroom

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

Khan Academy video wrapper

Evaluating an expression with one variableSee video transcript

Reflection question

What was Sal finding when he plugged t, equals, 10 into the expression 5, t, plus, 3?

Let's try a practice problem!

The expression 2, m, plus, 10, c gives the amount of money, in dollars, a dessert store makes from selling m muffins and c cakes.

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

dollars

Challenge problem

Part A

A flower store uses the expression 2, plus, 5, r to determine the cost, in dollars, of r roses.

Complete the table to find the cost of different numbers of roses.

Number of roses left parenthesis, r, right parenthesis	Cost left parenthesis, 2, plus, 5, r, right parenthesis
3	17
6	Your answer should be an integer, like 6 a simplified proper fraction, like 3, slash, 5 a simplified improper fraction, like 7, slash, 4 a mixed number, like 1, space, 3, slash, 4 an exact decimal, like 0, point, 75 a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text
9	Your answer should be an integer, like 6 a simplified proper fraction, like 3, slash, 5 a simplified improper fraction, like 7, slash, 4 a mixed number, like 1, space, 3, slash, 4 an exact decimal, like 0, point, 75 a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text

Part B

Cam has 32 dollars. How many roses can he afford to buy?
Assume that he wants to buy as many roses as he can.

Extra challenge

Explain to a family member, friend, or classmate why the cost of six roses is not double the cost of three roses.

[Give me a hint.]

Want to join the conversation?

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TrySmarter101
Posted 6 years ago. Direct link to TrySmarter101's post “This extra challenge has ...”
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.
Button navigates to signup pageComment on TrySmarter101's post “This extra challenge has ...”
(42 votes)
Answer
- Ian Pulizzotto
  Posted 6 years ago. Direct link to Ian Pulizzotto's post “The expression 2 + 5r for...”
  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!
  Comment on Ian Pulizzotto's post “The expression 2 + 5r for...”
  (40 votes)
Madelyn Paton
Posted 3 years ago. Direct link to Madelyn Paton's post “how do you find the value...”
how do you find the value of the muffins and cakes? it doesn't give enough info?
Button navigates to signup pageButton navigates to signup page
(9 votes)
Answer
- Denis Orlov
  Posted 3 years ago. Direct link to Denis Orlov's post “It gives all the info you...”
  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
  Comment on Denis Orlov's post “It gives all the info you...”
  (16 votes)
gmmkyingtao
Posted 4 months ago. Direct link to gmmkyingtao's post “the extra challenge is ma...”
the extra challenge is making me loose my brain cells
Button navigates to signup pageComment on gmmkyingtao's post “the extra challenge is ma...”
(12 votes)
Answer
- Ankara_Messi_Ankara_Messi
  Posted 3 months ago. Direct link to Ankara_Messi_Ankara_Messi's post “If the variable was multi...”
  If the variable was multiplied by 5 only then it would double but then if you add 2 it won't double.
  Button navigates to signup page
  (3 votes)
Nathaniel Lawrence
Posted 5 years ago. Direct link to Nathaniel Lawrence's post “can you explain 100+20(51...”
can you explain 100+20(51/4)
Button navigates to signup pageComment on Nathaniel Lawrence's post “can you explain 100+20(51...”
(5 votes)
Answer
- Kim Seidel
  Posted 5 years ago. Direct link to Kim Seidel's post “100+20(5 1/4) Follow orde...”
  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.
  Comment on Kim Seidel's post “100+20(5 1/4) Follow orde...”
  (6 votes)
Daniel Ungureanu
Posted 7 years ago. Direct link to Daniel Ungureanu's post “Cam has 32 dollars. How m...”
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.
Button navigates to signup pageButton navigates to signup page
(3 votes)
Answer
- wyojohn
  Posted 7 years ago. Direct link to wyojohn's post “If he buys 6 roses, the c...”
  If he buys 6 roses, the cost (from the formula in the problem) is 2 + 5r = 2 + 5(6) = 32.
  Comment on wyojohn's post “If he buys 6 roses, the c...”
  (8 votes)
Subnauticaplayer88
Posted 4 months ago. Direct link to Subnauticaplayer88's post “What does it mean mathema...”
What does it mean mathematically if you "plug something in"?
Button navigates to signup pageComment on Subnauticaplayer88's post “What does it mean mathema...”
(2 votes)
Answer
- Kim Seidel
  Posted 4 months ago. Direct link to Kim Seidel's post “It's called "substitution...”
  It's called "substitution". You replace one item with another of equal value.
  Comment on Kim Seidel's post “It's called "substitution...”
  (7 votes)
kmaeinc
Posted 5 years ago. Direct link to kmaeinc's post “What does the 2 signify i...”
What does the 2 signify in the equation 2+5r?
Button navigates to signup pageButton navigates to signup page
(4 votes)
Answer
- ＫＥＶＩＮ
  Posted 5 years ago. Direct link to ＫＥＶＩＮ's post “Here 2 is just 2! It's a ...”
  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.
  Comment on ＫＥＶＩＮ's post “Here 2 is just 2! It's a ...”
  (3 votes)
kcking
Posted 6 years ago. Direct link to kcking's post “what do I do on the extra...”
what do I do on the extra challenge?
Button navigates to signup pageButton navigates to signup page
(4 votes)
Answer
- Redapple8787
  Posted 6 years ago. Direct link to Redapple8787's post “Follow the instructions. ...”
  Follow the instructions. Explain why 2+5r is NOT equal to double of the cost of 3 roses.
  Comment on Redapple8787's post “Follow the instructions. ...”
  (3 votes)
tulipmitchell
Posted 3 years ago. Direct link to tulipmitchell's post “I have no idea how to do ...”
I have no idea how to do this. Can someone explain what he did in the video?
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(5 votes)
Answer
akawessa63
Posted 4 years ago. Direct link to akawessa63's post “I do not understand the s...”
I do not understand the second one the problem
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(5 votes)
Answer