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Standard arithmetic: + - * / %. Integer division when both operands are integers — 7 / 3 == 2. Mix in a float for a real result: 7.0 / 3 == 2.333….

a = 17
b = 5
puts a + b      # 22
puts a / b      # 3   (integer)
puts a.to_f / b # 3.4
puts a % b      # 2
puts 2 ** 10    # 1024 (power)

Numbers in Ruby have rich method APIs:

5.times { |i| puts i }       # 0 1 2 3 4
(1..3).each { |n| puts n }    # 1 2 3
puts 17.divmod(5)              # [3, 2] — quotient and remainder
puts 100.to_s(2)               # "1100100" — binary

Integers in Ruby are arbitrary precision — 1_000_000 ** 100 works without overflow.