50×50%=25 (person)

50×2/5=20 (person)

25+20-7=38 (person)

50-38= 12 (person) Answer: 50 volunteers and 12 window cleaners.

2. Put ***x baskets of cantaloupes

X-(50% x+50% x 3/5) = 1/5x A: 1/5 left.

3. 1-60%=40%

60%-40%=20%=400 pages A:* * * * 400 pages.

4.3/4+40%= 1 15%

1 15%- 100%= 15%

12÷ 15%=80 (person)

80×3/4=60 (person)

80×40%=32 (people) A: There are 60 people in the math group and 32 people in the Chinese group.

5.***3, one each.

6. solution: let this number be X.

1/2x=25%x+ 10

X =40 A: This number is 40.

7. (180-9/5× 45) ÷ 9/5 = 55 (km/h) Answer: 55 km/h.

8.100 ÷ (1-3/5) = 250 yuan-bookcase

250- 100= 150 (yuan)-bed

9. 16(3/5- 1/3)= 60 (page 1)

10.24÷ (1/3-1/4) = 288 (kg)

11.3× (5000× 5%) = 750 yuan for three years.

12. [24 ÷ (1-88%)] × 88% =176 (person)

13.200-[(200×10%) ÷16%] = 75 (g)

14.2 (11-10) = 2 (person)

2× 1 1=22 (person)

2× 10=20 (person)

15.5(4-3)= 5 (kg)

5× 4 = 20kg

16. 1: 1.3= 10: 13

17.15 ÷ (1/2-3/10) = 75 (km)

18.1÷ (1/4+1/6) =12/5 (when)

19. 1÷( 1/3+ 1/5)=8/ 15

20. 1/2+ 1/5+ 1/8+ 1/ 10=37/40

There are three people in 50×( 1-37/40)≈3 (person).

Hope to adopt