help with fraction question

Question

The four blades in a four-piece chisel set contain cutting-edge widths of 1/20, 1/5, 7/20 and 1
 Find the difference in the cutting-edge widths of the two chisels with the widest blades. The double prime symbol stands for inches.
Begin by determining which two chisels have the widest blades. To do so, rewrite all fractions as like fractions with the least common denominator, LCD, as their new denominator.

Answer 1

The smallest common denominator has to be as big as the biggest denominator, so we are looking at 20.  1/5 needs to be changed:what number can we multiply 5 by to get 20?  Well, 20/5 is 4, so 5 times 4 is twenty.  You multiply both the numerator and denominator by 4, and get 1/5 = 4/20.  1 is a whole, so it is 20/20.  The fractions are now 1/20,4/20. 7/20 and 20/20,

The largest two, then, are found by the ones that have the most twentieths, so they are 20/20 and 7/20.  I want to subtract the two fractions.  Since the denominators are the same, I just subtract the numerators.  

 20-7  = 13

   20       20

 

Hope that helped!  Keep working and remember to breathe!