2. Solution: The number of pears in this box is a multiple of 2, 1, a multiple of 3 and a multiple of 2 and 5, so after you add this number to 1, a+ 1 is a multiple of 2, a multiple of 3 and a multiple of 5.

That is, a+ 1 is at least the least common multiple of 2,3,5.

So by a+ 1 =2*3*5.

The solution is a=29.

That is, there are at least 29 pears.

3, this should be classified,

There are three * * * sides with the length of 1 = 9.

There are four sides with a length of 2.

There are 1 * * with a side length of 3.

An oblique square with four sides greater than 1 less than 2.

The side is longer than 2 and less than 3 (also an oblique square), and there are 2 in a * * *.

So a square has 9+4+ 1+4+2=20.

4, no equation is slightly difficult:

Because a class doesn't plant 40 trees, that is, classes 2 and 3,

Because Class 2, that is, 1 class and Class 3 didn't plant 50 trees,

Because class 3, that is, 1 class and class 2 didn't plant 60 trees,

If you add these up, it is 40+50+60= 150 trees, and the trees planted in each class are counted twice.

Therefore, the total number of trees is: (40+50+60)/2=75.

thank you