(1 + 9/10 + 3/4 + 1/2)
20/20+18/20+15/20+10/20=63/20=3.15
I would have tried to do it more simply - or just use a calc.
1 + 9/10 + 3/4 + 1/2
= 1+3/4 +1/2 + 9/10
=1+1 +1/4 +9/10
=2.25+0.9
=3.15
=3 15/100 = 3 and 3/20