He cost, c, of a health club membership is related linearly to its length in months, m. If a 12-month membership costs $260 and an 18-month membership costs $380, which equation can be used to find the cost of a 30-month membership?

A) c - 380 = 1/20 (30-18)

B) c - 18 = 20 (380-30)

C) c - 380 = 20 (30-18)

D) c - 18 = 20 (30-12)

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Mathematics

13 July, 00:19

He cost, c, of a health club membership is related linearly to its length in months, m. If a 12-month membership costs $260 and an 18-month membership costs $380, which equation can be used to find the cost of a 30-month membership?

A) c - 380 = 1/20 (30-18)

B) c - 18 = 20 (380-30)

C) c - 380 = 20 (30-18)

D) c - 18 = 20 (30-12)

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Answers (1)

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Bullet · Answer 1

Treat the c formula as a line. c = sm + b; where m = number of months.

using the two examples:

260 = 12s + b

380 = 18s + b

solve for s & b:

s = 20

b = 20

So a 30-month membership is:

c = 20 (30) + 20 = 600

Solve C for c and you get 600