The cost of dinner for a group of students is partly constant and partly varies…

The cost of dinner for a group of students is partly constant and partly varies directly as the number of students. If the cost is N74.00 when the number of is 20 and N96.00 when the number is 30, find the cost when there are 15 students

Correct Answer: Option B

Explanation

C = a + kS. If C = 74, S = 20

C = 96, S = 30, C= ? S = 15

74 = a + 20k……(1)

96 = a + 30k……(2)

subtract equation (1) from (2)

96 = a + 30k
–
74 = a + 20k
——-
22 = 10k

k = 2.2

find a

74 = a + 44

a = 30

C = 30 + 2.2S

when S = 15, C = 30 + 2.2 x 15

= 30 + 33

= N63