Answer:
a. The number of DVDs is 10 - c
b. The cost of the CDs is 12c
c. The cost of the DVDs is 20(10 - c)
d. The total cost of all gifts is 200 - 8c
Step-by-step explanation:
* <em>Lets explain how to solve the problem</em>
- You are buying gifts for 10 people
# You will buy 10 gifts
- The gifts are CD or DVD
# The total numbers of CDs and DVDs is 10
- The cost of each CD is $12 and the cost of each DVD is $20
a.
# c is the number of CDs
∵ You buy c CDs
∵ The total numbers of CDs and DVDs is 10 as we said up
∴ c + the numbers of DVDs = 10
- Subtract c from both sides
∴ The number of DVDs = 10 - c
* The number of DVDs is 10 - c
b.
∵ The number if CDs is c
∵ The cost of each CD is $12
∴ The cost of the CDs = 12 × c = 12c
* The cost of the CDs is 12c
c.
∵ The number of DVDs is 10 - c
∵ The cost of each DVD is $20
∴ The cost of the DVDs = 20(10 - c)
* The cost of the DVDs is 20(10 - c)
d.
∵ The cost of the CDs is 12c
∵ The cost of the DVDs is 20(10 - c)
- The total cost of all the gifts is the sum of the costs of CDs and DVDs
∴ The total cost of all gifts = 12c + 20(10 - c)
- Multiply the bracket by 20
∵ 20(10 - c) = 100(2) - 20(c) = 200 - 20c
∴ The total cost of all gifts = 12c + 200 - 20c
- Add like terms
∴ The total cost of all gifts = 200 - 8c
* The total cost of all gifts is 200 - 8c
