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).

Q: What is 0 + 5 - 15 - -5?

A: -5
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Q: What is 51/2 of a millisecond in microseconds?

A: 25500
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Q: What is prob of sequence rr when two letters picked without replacement from {r: 8, x: 3}?

A:
28/55
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