Because there are less than 50 people in Class A, but not less than 40 people, there should be 24 tickets per person in Class A..

At the same time, the number of people in class B should be more than 50, but less than 100, so each person in class B should be 2 1 yen.

So there is 24x+21(105-x) = 2349.

Solve x = 48, 105-x = 57.

So there are 48 students in Class A and 57 students in Class B..

After the joint ticket purchase, each person's ticket is 18 yuan, so each person in Class A saves 24- 18=6 yuan, and each person in Class B saves 2 1- 18=3.

So class A saved 6*48=288 yuan, and class B saved 3*57= 17 1 yuan.

2. You can buy X balls in Store A,

Know from the meaning of the question

90=30*2*90%+2x*90%

Solve x=20

B shop can buy y balls.

According to the meaning of the question

90=30*2+2y

Solve y= 15

Buy another racket and get two balls, then you can get 15+4= 19 balls in store B.

So it's a good deal to buy it at a shop.

3. let the speed of the plane be x when there is no wind.

According to the meaning of the question, the speed is =x+24 with the wind, and the speed is =x-24 with the wind.

So (x+24)*5.5=(x-24)*6.

Solve x=552

So the distance between Party A and Party B is (552+24) * 5.5 = 3 168km.

4. Let the single digit of this two-digit number be X and the decimal number be 7-X..

According to the meaning, there is

(7-x)* 10+x+45 = x * 10+(7-x)

Solve x=6

So the single digit is 6, the ten digit is 1, that is, the two digit is 16.