Lauren bought 20 ounces of ham. She used 3/4 of the ham to make sandwiches for her friends and 1/5 of the ham in an omlete. How many ounces of ham were left?

Lets divide the problem in parts, first for sandwiches she used 3/4 out of 20 ounces of ham:

(3/4) (20) = 60/4 = 15

so for sandwiches Lauren used 15 ounces

Then for omelete she used 1/5, that is:

(1/5) (20) = 20/5 = 4

then Lauren used 4 ounces for omelete

So Lauren used 15 ounces for sandwiches and 4 ounces for omelete, that is 19 ounces in total, so there are left from the 20 original ounces:

20 - 19 = 1

there is 1 ounce of ham left