1. Suppose there are x cars for small cars and 50-X cars for medium cars.

Then 6(50-x)+4x=230.

Get x=35.

∴50-x= 15

2. Solution: Suppose you bought X copies for the first time and Y copies for the second time.

x+y=30

0.9*5x+0.7*5y= 1 13

The solution is x=8 y=22.

3. According to the meaning of the question: 55- 13=42 student donations1the number of 0 yuan or 20 yuan * *1180-5 * 6-50 * 7 = 800 yuan.

Let the decimal student be x and the twentieth student be Y: X+Y=42 10X+20Y=800.

Solution: X= 4 Y=38

So: Donation (RMB) 5 10 20 50

Number of people (persons) 6 (4) (38) 7