2. Suppose there are X students in Grade One, X+X-40 = 1000, and X = 480 students.
3. Set the first excavator to dig xm every hour? Second, dig x-40m? ,
16x+24(x-40)=8640，x=240m？ x-40=200 m？
4. Let a * * have x elements, (2x/7+16000) * (1/2)+2x/7+6000 = x, x = 42000 A gives 2x/7= 12000, and b gives.
5.x+ 1=(5x/6)* 1.5, uphill speed x=4 downhill speed 1.5x=6 total distance s=4+ 1=5km.
6.900*0.8-x*20%，x=600
7. Let the unit number be X, (10x+x/2)-(10x/2+x) = 36, x = 8, and the original number is 48.
8. Suppose people walk for t hours, 60 (t- 1)+5t = 2 * 60, t = 36/ 13 hours.
9.( 1/3)pi(300/2)^2*8=pi( 100/2)^2*h，h=24cm
10. Let the original selling price be x, x * 0.8-1200 =1200 *14%, and X = 17 10.
1 1. If the total workload is 1 and each person completes (3/5)/( 14*9) every day, there will be ((3/5)/(14 * 9)) * x *.
X=2 1 person
12. let the scheduled period be x days, 20x+100 = 20 (1+25%) x-50, and X = 30. The number of parts originally planned to be produced is s=30+20+ 100=700.
The scheduled period is 30 days.
13. Let Xiaoming's cycling speed be x, 0.5x+0.5 * 2x = 30, and x = 20km/h..