JAMB - Mathematics (1989 - No. 14)
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 students is 20 and N96.00 when the number of students is 30, find the cost when there are 15 students
N68.50
N63.00
N60.00
N52.00
Explication
where C = cost, S = number of students, a and K are constants.
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