Given a simple high-school level math question, you are required to solve it and provide the final answer. The final answer is always a single number. These questions can range from a variety of topics like simple arithmetic, solving equations, converting a quantity from one unit to another, finding remainders/GCD/LCM, finding probabilities etc. Each question has only one correct answer. This answer can be a positive or negative integer, a fraction or a decimal number. If the answer is a negative number use the hyphen (e.g. -42) symbol for the minus sign. For decimal numbers, do not add extra zeros after the decimal point. For fractional numbers, separate the numerator and denominator using a forward slash (e.g. 3/25).
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Question: Calculate prob of sequence pb when two letters picked without replacement from aapbbpppbpppbabab.

Answer: 21/136


Question: Let x be (36/(-20))/((-3)/15). Let r(z) = z**2 - 8*z - 5. Let h be r(x). Solve -k + w + 0 - 2 = 0, -h*k - 2*w + 22 = 0 for k.

Answer: 3


Question: How many micrometers are there in 21/4 of a millimeter?

Answer:
5250