1.(2 15- 180 )÷ 1200

=35 ÷ 1200

≈29.2%

The number of students has decreased. It has decreased by about 29.2%.

2. 15÷( 1+20%)

= 15÷ 1.2

= 12.5 m2

A: The per capita housing area in 200 1 year is 12.5 square meters.

3.24 present 75% = 32 (yuan)

A: The original price is 32 yuan.

4. 1200÷(40%-30%)

= 1200÷0. 1

= 12000 (yuan)

A: The school has 12000 books.

5.30000×3. 14%×3

=942×5

=47 10 (yuan)

47 10>4500

When it expires in 2006, he can buy this computer with interest.

6.0 -2 +2 + 1 - 1

7. Shortcuts (it's hard to type on a computer)

8. The first air: 26: 5 and the second air: 26/25.

9. One and a fifth

(2) 6: 5 1/5

(3) 36:25 1.44

10.2+ 1=3

450×2/3=300 (g)

450× 1/3= 150 (g)

A: 300 grams of leek, eggs 150 grams.

1 1.40000:50000

= 4:5

4+5=9

45000×4/9=20000 (yuan)

4500×5/9=25000 (yuan)

Chen Ming got 20 thousand yuan. Zhao Dong got 25,000 yuan.

12.

( 1) 180÷( 1 1-8)

= 180÷3

=60 km

(2) ellipsis.

Space and graphics

13.

14. 12×20=240 (m2)

3. 14×4?

=3. 14× 16

=50.24(㎡)

240-50.24= 189.76(㎡)

Answer: The lawn covers an area of 189.76㎡.

15. Naughty distance: 8*4=32 (m)

Distance to smile: 8*3. 14=25. 12 (m)

32>25. 12

Answer: Smile and walk around first.

16.

17.

18.3.14× 40 =125.6 (cm)

125.6cm = 1.256m

3 1.4÷ 1.256=25 (weeks)

A: The wheel will turn 25 times.

19~24.

(Too many, you don't give points, no one answers, or I kindly help you answer, and my hands are sore. I have to accept it. I suggest you buy a one-stop book, 10, with complete answers. Downstairs, don't copy! ! Shit, why are you so cheap downstairs? Do you know how many words I have to type? Bitch, garbage. Please compare our answer time, I answered first! ! )