Answer:
Step-by-step explanation:
draw Venn diagram
passed test ---- both - did assignment
20-16=4 -------- 16 -------- 19-16 = 3
4 + 16 + 3 = 23 who did something useful
that leaves 28 - 23 = 5 outside your diagram who did nothing
16 out of the 19 who did the homework passed the test
so
16/19 = 0.842