https://paiza.jp/poh/enkoi #2

enkoi-2.rb

# 自分の得意な言語で
# Let's チャレンジ！！
 
# Normal way
=begin

sum = 0
# first input is the count of lines
gets.to_i.times do
    required, now, price = gets.split(" ").map{|i| i.to_i}
    # make it no smaller than 0
    sum += [required - now, 0].max * price
end
puts sum

=end
 
# Rubyは怖いです
puts gets.to_i.times.map {
        required, now, price = gets.split(" ").map{|i| i.to_i}
        [required - now, 0].max * price
    }.inject(&:+)