A bike costing $⁢400 is bought using a credit card with a 20% annual interest rate. If the full payment is made within a 30 -day grace period, what is the total cost of the bike? Formula: total cost=purchase amount+(purchase amount⋅interest rate)

A credit card’s 30-day grace period means no interest is charged if the balance is paid in full during that period. So the total cost is the $400 purchase price, with $0 interest: $400 + $0 = $400. The correct choice is 400 dollars.

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