def driver_check(age, road_test):
    '''can drive if you've passed the road test and are at least 16,
    if not passed road test, can still get a permit if at least 15'''
    if road_test:
        print("yes, can drive")
    elif age >= 15:
        print("learner's permit only")
    else:
        print("no, can't drive")
    
def water_type(temp):
    '''return 'solid', 'liquid', or 'gas' depending on water temp.
    colder than 32 is ice, warmer than 212 is gas'''
    if temp < 32:
        return 'solid'
    elif temp < 212:
        return 'liquid'
    else:
        return 'gas'

def letter_grade(score):
    '''return the letter grade corresponding to the given score'''   
    if score >= 90:
        return 'A'
    elif score >= 80:
        return 'B'    
    elif score >= 70:
        return 'C'
    elif score >= 60:
        return 'D'
    else:
        return 'F'

def effective_tax(income):
    '''return effective tax rate given the following marginal tax rates:
    0% up to $10k
    10% up to $30k
    25% up to $60k
    35% up to $100k
    50% over $100k'''
    taxes = 0
    remaining = income
    if remaining > 100000:
        # we have income to tax at 50%
        margin = remaining - 100000
        taxes += margin * 0.5
        remaining = 100000
    if remaining > 60000:
        # we have income to tax at 35%
        margin = remaining - 60000
        taxes += margin * 0.35
        remaining = 60000
    if remaining > 30000:
        # income to tax at 25%
        margin = remaining - 30000
        taxes += margin * 0.25
        remaining = 30000
    if remaining > 10000:
        # income to tax at 10%
        margin = remaining - 10000
        taxes += margin * 0.1
    # ignore the last 10000 (no tax)

    # compute the effective tax rate using total tax
    return taxes / income