[gkesden@ghc43 ~]$ irb
irb(main):001:0> 15 + 110
=> 125
irb(main):002:0> 15 - 110
=> -95
irb(main):003:0> 15 * 110
=> 1650
irb(main):004:0> 15 / 110
=> 0
irb(main):005:0> 15.0 / 110.0
=> 0.136363636363636
irb(main):006:0> 15.0 / 110
=> 0.136363636363636
irb(main):007:0> 99 / 100
=> 0
irb(main):008:0> 1.0 / 3.0
=> 0.333333333333333
irb(main):009:0> 2.0 / 3.0
=> 0.666666666666667
irb(main):010:0> 7.0 / 9.0
=> 0.777777777777778
irb(main):011:0> 110 % 15
=> 5
irb(main):012:0> 42 % 18
=> 6
irb(main):013:0> 42 % 6
=> 0
irb(main):014:0> 17 % 2
=> 1
irb(main):015:0> 18 % 2
=> 0
irb(main):016:0> 19 % 2
=> 1
irb(main):017:0> 20 % 2
=> 0
irb(main):018:0> 15 % 110
=> 15
irb(main):019:0> 5 ** 3
=> 125
irb(main):020:0> 8 ** 2.4
=> 147.03338943962
irb(main):021:0> 9 ** 0.5
=> 3.0
irb(main):022:0> 9 ** (1/2)
=> 1
irb(main):023:0> 27 ** (1.0/3.0)
=> 3.0
irb(main):024:0> 5 * 6 + 7
=> 37
irb(main):025:0> 5 * (6 + 7)
=> 65
irb(main):026:0> 3 * 4 / 5
=> 2
irb(main):027:0> 3 * (4 / 5)
=> 0
irb(main):028:0> 2 ** 3 ** 4
=> 2417851639229258349412352
irb(main):029:0> (2 ** 3) ** 4
=> 4096
irb(main):030:0> x = 6
=> 6
irb(main):031:0> y = 14.5
=> 14.5
irb(main):032:0> z = 42 % 18
=> 6
irb(main):033:0> x
=> 6
irb(main):034:0> y
=> 14.5
irb(main):035:0> x + z
=> 12
irb(main):036:0> gravity = 9.8
=> 9.8
irb(main):037:0> interest_rate = 0.015
=> 0.015
irb(main):038:0> 7up = 2.39
SyntaxError: compile error
(irb):38: syntax error
7up = 2.39
   ^
        from (irb):38
        from :0
irb(main):039:0> courseFall2011 = 15110
=> 15110
irb(main):040:0> gravity
=> 9.8
irb(main):041:0> gravitY
NameError: undefined local variable or method `gravitY' for 

main:Object
        from (irb):41
        from :0
irb(main):042:0> base = 15
=> 15
irb(main):043:0> height = 110
=> 110
irb(main):044:0> triangle_area = 0.5 * base * height
=> 825.0
irb(main):045:0> base = 20
=> 20
irb(main):046:0> triangle_area = 0.5 * base * height
=> 1100.0
irb(main):047:0> base = 25
=> 25
irb(main):048:0> triangle_area
=> 1100.0
irb(main):049:0> triangle_area = 0.5 * base * height
=> 1375.0
irb(main):050:0> course = 15110
=> 15110
irb(main):051:0> course + 2
=> 15112
irb(main):052:0> course = "15110"
=> "15110"
irb(main):053:0> course + 2
TypeError: can't convert Fixnum into String
        from (irb):53:in `+'
        from (irb):53
        from :0
irb(main):054:0> s1 = " "
=> " "
irb(main):055:0> s2 = ""
=> ""
irb(main):056:0> male = true
=> true
irb(main):057:0> married = false
=> false
irb(main):058:0> f = 32
=> 32
irb(main):059:0> c = 5/9 * (f-32)
=> 0
irb(main):060:0> f = 80
=> 80
irb(main):061:0> c = 5/9 * (f-32)
=> 0
irb(main):062:0> c = (5.0/9.0) * (f-32)
=> 26.6666666666667
irb(main):063:0> side = 109
=> 109
irb(main):064:0> square = side * side
=> 11881
irb(main):065:0> triangle = 0.5 * side / 2 * side / 2
=> 1485.125
irb(main):066:0> area = square - triangle
=> 10395.875

At this point, I use vi to create a 
Ruby file that contained one function
that computes the area of a countertop
that is in the shape of a square:

def compute_area(side)
    area = side * side
    return area
end

I saved the file as "computearea.rb".

In this function definition, there is one
parameter, side. When we call this function,
we need to supply one value for the side.
It returns the answer back to wherever we
call the function (in this case, irb).

In irb again:

irb(main):067:0> load "countertop.rb"
=> true
irb(main):068:0> compute_area(15)
=> 225
irb(main):069:0> compute_area(110)
=> 12100
irb(main):070:0> x = 42
=> 42
irb(main):071:0> compute_area(x)
=> 1764
irb(main):072:0> compute_area(15) + compute_area(110)
=> 12325

Using the Math module:

irb(main):077:0> Math.sqrt(16)
=> 4.0
irb(main):078:0> Math.log10(100.0)
=> 2.0
irb(main):079:0> Math::PI
=> 3.14159265358979
irb(main):080:0> Math.sin(Math::PI / 2)
=> 1.0
irb(main):081:0> include Math
=> Object
irb(main):082:0> sqrt(16)
=> 4.0
irb(main):083:0> PI
=> 3.14159265358979
irb(main):084:0> quit

1G