Solution: suppose the speed of the spacecraft is x km/s.

40/57x=8

40/57x÷40/57=8÷40/57

x=57/5

Solution 2

8÷40/57=57/5 (km/s)

4.

Solution: let this bucket weigh x kilograms.

x- 1/ 10x=9

( 1- 1/ 10)x=9

x=9÷9/ 10

x= 10

or

9÷ (1-110) =10 (kg)

5.

15/ 16÷3= 15/ 16× 1/5=3/ 16

12/25÷8= 12/25× 1/8=3/50

8÷4/5=8×4/5= 10

2 1/40÷7/8=2 1/40×8/7=3/5

16÷2/ 17= 16× 17/2= 136

7/24÷6/49=7/24× 17/2=343/ 144

18/35÷0.6×2/3

4/9× 15/ 16÷5/6

=35/ 18

× 10/6×2/3

=5/ 12×6/5

=6/7×

2/3

= 1/2

= 12/2 1=4/7

(

2-0.6)÷7/ 15

35/64÷( 1/8+3/4)

= 1.4× 15/7

=35/64÷7/8

=3

=35/64×8/7

=5/8