2 & gt 15/[( 1/2+3/8)*5/ 14]= 15/(7/8*5/ 14)= 15* 14*8/(7*5)=3*2*8=6*8=48

3> small class150 * (1-40%) * 4/(4+5) = 40, middle class150 * (1-40%)-40 = 50.

4 & gt 16/( 1/25%- 1/45%) = 16/[ 100 ( 1/25- 1/45)] = 65438.

5 & gt6-[ 1-6 * ( 1/ 15+ 1/20)]/( 1/30) = 6-30 * ( 1-6 * 7/60).

6> (360 * 2-0.5 * 40)/(40+60) = 700/100 = 7 hours.

7> 277/0.9 = 307.8,2000 * 20%-307.8 = 92.2,92.2/(20%-10%) = 922. The cost of A is 922 yuan, and the cost of B is 1078 yuan.

8> Now each pile is 48/3= 16, the first pile is 16/2=8, the third pile is 8+ 16=24, and the second pile is 16+24/2=28. The first pile 8+28/2=22, the second pile 28/2= 14, and the third pile 24/2= 12.

9 & GT20/2-(3-1) (20/2-8) =10-4 = 6 minutes.

10 >C.4/5=80%

1 1 & gt； 3 2 = 9 times

12 >[(2/40%)/4- 1]/[(2/40%)/4]= 1/4 / 5/4=20%

13 > let the velocities be x and y respectively, then R=(x+y)t=(x-y)r x/y=(t+r)/(t-r).

14 & gt； The length, width and height of the rectangle are 3, 1 2, respectively, and the surface area is 2 * (3 *1+3 * 2+1* 2) = 2 *1= 22.

15 >3/4 * 2/5=3/ 10

16 > 1+28+2+ 14+4+7=56

17 > 500-(950-500) = 500-450 = 50 people, 50/500= 10%, 500/950 = 52.6%,1-52.6% =

18 & gt； (36/2)/3=6 cm

19 > 6 * 2 =12kg

20 >； B 81(1+1+1/4) = 81(9/4) = 36 years old, and A 8 1-36=45 years old.

2 1 & gt； 2 18

22 >； [60*2/(2-20/60)-60]/60=(72-60)/60= 12/60=20%