Challenge 1: A select + map Pipeline — Solution

numbers = (1..20).to_a

result = numbers
  .select { |n| n % 3 == 0 }
  .map { |n| n * n }

puts result.inspect

=begin
Output:
[9, 36, 81, 144, 225, 324]

Notes:
- (1..20).to_a converts the Range into an actual Array so it's clear
  Enumerable methods work identically on both.
- .select { |n| n % 3 == 0 } keeps only the multiples of 3: [3, 6, 9, 12,
  15, 18].
- .map { |n| n * n } then squares each surviving number, producing the
  final array: [9, 36, 81, 144, 225, 324].
- Chaining .select then .map reads as one pipeline — "keep the multiples
  of 3, then square them" — without a temporary variable in between.
=end