so.. is 10 'in' 10..100? is 100?
To be clear, 10...100 includes 10, but not 100. So, it includes one bound: the one mentioned first, the lower bound.
(10...100).to_a
=> [10, 11, 12, 13, ... 98, 99] [1] pry(main)> 10..100
=> 10..100
[2] pry(main)> (10..100).class
=> Range
[3] pry(main)> (10..100).to_a
=> [10, 11, 12, 13, 14, ..., 99, 100]