10/3 x 4/5 = 8/3
two and two fifths
3/10
four fifth's times two is eight fifths (8/5) which is the same as one and three fifths (1 3/5)
Twenty four fifths is four and four fifths. So if you take three away, that leaves one and four fifths.
52/5
Four fifths times 5 is 20 fifths which is equal to 4.
2 fourths times four fifths is 2 fifths.
3/40
1.6
four fifths is bigger
5 is 25 fifths, 3 x 4 fifths is 12 fifths so difference is 13 fifths or 2.6 or two and three fifths.
Estimating 5 and 9/10ths times 2 and 2/3rds might be done by considering that 5 and 9/10ths is about 6, and 2 and 2/3rds is somewhat less than three. Six times three is eighteen, but it's less than that by a couple or three, so the answer is about fifteen or sixteen.