#5
57.8 can be rounded to 60 because 57.8 is closer to 60 than 50 and 81 is relatively close to 80. if we had to estimate the quotient, we would have
60 ÷ 80 = 0.75
#8
2.8 can be rounded to 3 because 2.8 is closer to 3 than it is to 2 and 6 can be left alone because it will make our division easier.
3 ÷ 6 = 0.5
#11
737.5 can be rounded to 700 and 9 can be rounded to 10.
700 ÷ 10 = 100
