2, pear tree 60*5/4=75.

3. pear tree 60*( 1- 1/5)=48.

4. pear tree 60*( 1- 1/4)=45.

5. There are 40 cocks and 0 hens 100.

Equation: 1-4, let x pear trees:

1、x/60=4/5，x=48

2、x/60=5/4，x=75

3、x/60= 1- 1/5，x=48

4、x/60= 1- 1/4，x=45

5. Let the cock be X and the hen be Y, then: x/y=2/5, x+60=y, x=40, y= 100.

Do you understand? Think more! Students, come on!