import math

# setup situation
bag1 = ['r']*4 + ['b']*5    # 1 pick
bag2 = ['r']*3 + ['b']*7    # 2 picks
                            # b b r

# initialize counting variables
numerator = 0
denominator = 0

# collect event occurrences
for X in bag1:  # 1 pick from bag1
    
    for Y1 in bag2:  # 1 pick from bag2
        bag2reduced = bag2.copy()  # create a COPY of bag2
        bag2reduced.remove(Y1)  # remove already picked element from COPY of bag2
        
        for Y2 in bag2reduced:  # 1 pick from EDITED bag2
            tup = (X, Y1, Y2)  # event
            
            if all([tup.count('r') == 1,
                    tup.count('b') == 2]):  # conditions of interest
                numerator += 1
            
            denominator += 1

gcd = math.gcd(numerator, denominator)

numerator //= gcd
denominator //= gcd

print(f'{numerator}/{denominator}')