5.7.6 hours

9.C

10. 160 yuan

1 1. solution: let this batch of parts have x pieces.

x/ 100-x/( 100+ 10)= 2

( 1 1- 10)/ 1 100×X = 2

X=2200

2200÷ 100=22 (days)

12. Solution: Let it fill in x minutes.

x×(( 1/45)+( 1/60)+( 1/90))= 1

( 1/20)X= 1

X=20

13.( 1) solution: let the first set of costs be x yuan. Suppose: the cost of the second set is Y yuan.

( 1+20%)X = 168( 1-20%)Y = 168

1.2X = 168 0.8Y = 168

X= 140 Y=2 10

(2) (140+210)-168× 2 =14 (yuan)