A used book store is selling 3 records and 5 CDs for $60. You can also buy 6 records and 4 CDs for $80. Find the cost of one CD. Write the linear system that describes this situation.​

9514 1404 393

  3r +5c = 60

  6r +4c = 80

Step-by-step explanation:

There are many aspects of "this situation" that could be described by equations. We are guessing that you want equations that will help you determine the costs of a record and a CD, assuming the costs are the same for each instance of the media.

Let r and c represent the costs of a record and a CD, respectively.

  3r +5c = 60 . . . . . . . the value of the first purchase

  6r +4c = 80 . . . . . . . the value of the second purchase

These equations comprise a linear system describing an aspect of the situation.

Comment on the question

The numbers make no sense, as the cost of a CD is $(6 2/3), the cost of a record is $(8 8/9).

were is the equation

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.