A store charges their customers based on the number of items that they buy. Jane bought four items and was charged $15 and George bought twelve items and was charged $39. Write a function to model the cost based on the number of items you buy. Then determine how much you bought if you were charged $33.

A)
f(x) = 3x + 3; f(10) = 33
B)
f(x) = 3x + 3; f(33) = 102
C)
f(x) =
1
3
x + 3; f(90) = 33
D)
f(x) =
1
3
x + 3; f(33) = 14

Question

A store charges their customers based on the number of items that they buy. Jane bought four items and was charged $15 and George bought twelve items and was charged $39. Write a function to model the cost based on the number of items you buy. Then determine how much you bought if you were charged $33.
	
A)
f(x) = 3x + 3; f(10) = 33	
B)
f(x) = 3x + 3; f(33) = 102	
C)
f(x) = 
1
3
x + 3; f(90) = 33	
D)
f(x) = 
1
3
x + 3; f(33) = 14

mathstudent55 · Answer

Use the points (4, 15) and (12, 39) and find the equation of the line that passes through them.

anonymous · Answer

@mathstudent55 This is a word problem, please read above, there is nothing to do with graphs here.

anonymous · Answer

@phi

phi · Answer

mathstudent gave you a good idea.

anonymous · Answer

not really i am totally lost can you explain

mathstudent55 · Answer

If I read the problem correctly, it asks you to "Write a function to model the cost based on the number of items you buy."

mathstudent55 · Answer

Since you are given information for two instances of purchases, matching one number of items to a price and a second number of items to another price, these are two points on a line. The function they are looking for has the equation of a straight line. If you use the given information, find the equation of the line. Then once you have the function, set the function equal to 33 and solve for x, to see what number of items corresponds to $33.

anonymous · Answer

would that be 10

phi · Answer

yes

anonymous · Answer

Thank you