Timmy and His Dad

    15) Though it takes young Timmy 3 hours to do all the yard work,
his father can do the same in 2 hours.  If they both work together,
how long will it take?

    1     1        1
  ---- + ----  =  ----
    3     2        x

    Since it takes Timmy 3 hours to do the yard work, then he
can do 1/3 of it in 1 hour.

    Find the lowest common denominator:

    L.C.D. = 6x

    6x (1)     6x (1)    6x (1)
       ---  +     ---  =    ---
        3          2         x

    Working each fraction:

    6x/3 = 2x
    2x * 1 = 2x
   
    6x/2 = 3x  
    3x * 1 = 3x
   
    6x/x = 6
    6 * 1 = 6

    2x + 3x = 6

    5x = 6

    x =  1.2 hours, or 1 and 1/5 hours, or 1 hour and  12 minutes.

    NOTE: To figure out the minutes from a decimal number, simply
multiply it by 60:  e.g. 0.2 * 60 =  12