It depends on what a quster is!
One half minus one fifth is 3 tenths
1 and 3 fifth
1 fifth
one fifth
7.5 out of a hundred
One fifth is two tenths. 8 tenths minus 2 tenths is 6 tenths or 3 fifths.
1/3 minus 1/5 is 2/15
1/2 minus 1/5 = 3/10
1/4 minus 1/5 is 1/20.
21
0.55
1/30th