it's 3/20!
Explanation:
start with 1 as the total number of school lunches.
to find the fraction of dumplings made, subtract the two other fractions from 1, so:
1 - (1/4 + 3/5) = # of dumplings
first make a common denominator for 1/4 and 3/5:
= 1 - (5/20 + 12/20)
= 1 - (17/20)
then, rewrite 1 as a fraction with 20 as the denominator:
= 20/20 - 17/20
= 3/20
and you can't simply this fraction further therefore the fraction of school lunches that are dumplings is 3/20
