600-1-3.py

def calc_paid_off(balance, interest_rate, payment):
    for month in xrange(12):
        balance = round(balance * (1 + interest_rate / 12.0) - payment, 2)
    return balance

initial_balance = float(raw_input("Enter the outstanding balance on your credit card: "))
interest_rate = float(raw_input("Enter the annual credit card interest rate as a decimal: "))
print "RESULT"

lower = initial_balance / 12.0
upper = (initial_balance * (1 + (interest_rate / 12.0)) ** 12.0) / 12.0
guess = 0

while True:
    guess = round((lower + upper) / 2.0, 2)
    result = calc_paid_off(initial_balance, interest_rate, guess)
    if abs(result) < 0.12:
        print "Monthly payment to pay off debt in 1 year: $%s" % guess
        print "Number of months needed: 12"
        print "Balance: $%s" % result
        break

    if result < 0:
        upper = guess
    elif result > 0:
        lower = guess