In: Finance
A bookstore offers you the following deal: you pay $31 today (in January) and you get 5%
off the price of everything you purchase in December (for simplicity assume exactly 12
months from now). If your savings account earns 4.50% APR (compounded monthly), how
much do you have to buy in December to just break even on the offer?
You pay today in January (PV) = $31
Interest rate (r)= 4.50% p.a. compounded monthly
Time (t)= 12 months
FV = PV * (1+r/12)12
FV= 31*(1+4.50%/12)12
FV = $32.4235
Since there is 5% off the price you purchase in December. Let us assume you buy ‘X’ in December and in order to break even on the offer:
X*(1-5%) = 32.4235
X= $34.13
You have to buy $34.13 in December to break even on the offer.