inject example(fibonacci,factorial)

### plus from min to max ###
2.0.0-p598 :018 > def fib(min,max)
2.0.0-p598 :019?>   a=min.upto(max).inject(:+)
2.0.0-p598 :020?>   a
2.0.0-p598 :021?>   end
 => nil
2.0.0-p598 :022 > fib(1,4)
 => 10
2.0.0-p598 :023 > fib(-1,4)
 => 9


### multiple from min to max###
2.0.0-p598 :028 > def fact(min,max)
2.0.0-p598 :029?>   a = min.upto(max).inject(:*)
2.0.0-p598 :030?>   a
2.0.0-p598 :031?>   end
 => nil
2.0.0-p598 :032 > fib(1,4)
 => 10
2.0.0-p598 :033 > fact(1,4)
 => 24

Very simple....