You are supposed to identify the category of a high-school level math question. There are five possible categories (1) algebra (2) arithmetic (3) measurement (4) numbers, and (5) probability. Use the following guidelines: (1) 'algebra' questions will typically contain letter variables and will ask you to find the value of a variable (2) 'arithmetic' questions will ask the sum, difference, multiplication, division, power, square root or value of expressions involving brackets (3) 'measurement' questions are questions that ask to convert a quantity from some unit to some other unit (4) 'numbers' questions will be about bases, remainders, divisors, GCD, LCM etc. (5) 'probability' questions will ask about the probability of the occurrence of something. A question must belong to only one category.

Example Input: What is prob of sequence rr when two letters picked without replacement from {r: 8, x: 3}?
Example Output: probability

Example Input: Suppose b + 3*k - 19 = 0, -4*b - 6*k = -4*k - 56. Calculate the remainder when 24 is divided by b.
Example Output: numbers

Example Input: Four letters picked without replacement from oikkxxooxkoxkxk. What is prob of picking 4 x?
Example Output:
probability