Barbara buys a box of pens for $4. For every additional box she buys, she gets a $1 discount. Which expression represents the total cost of the pens, c, as a function of the number of boxes, b?
c = f(b) = 4b – 1
c = f(b) = 4b + 1
c = f(b) = 3b + 4
c = f(b) = 4b + 3
c = f(b) = 4 + 3(b – 1)

Question

Barbara buys a box of pens for $4. For every additional box she buys, she gets a $1 discount. Which expression represents the total cost of the pens, c, as a function of the number of boxes, b?
c = f(b) = 4b – 1
c = f(b) = 4b + 1
c = f(b) = 3b + 4
c = f(b) = 4b + 3
c = f(b) = 4 + 3(b – 1)

anonymous · Answer

If Barb bought only one box, what did she pay? If she bought 2 boxes, what did she pay? If she bought 10 boxes, what did she pay? Each of these situations identifies a value for b and the corresponding value for c. Use these values in each alternative one-at-a-time until you find the one that fits in all situations. (Not my response, credit to ncruz) http://openstudy.com/study#/updates/554a87fae4b0b44c3ea7bad6