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: Three letters picked without replacement from {s: 5, f: 4, l: 1}. What is prob of picking 2 f and 1 l?

Answer: 1/20


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

Answer: -5


Question: What is prob of sequence tww when three letters picked without replacement from wtwfttaltatlttttlla?

Answer:
1/323