Difficult math problems in elementary school, math problems in primary school are very difficult

In order to carry out sports activities, the class used the class fee to buy basketball and volleyball. It is known that it costs 274 yuan to buy 3 basketballs and 2 volleyballs; It costs 478 yuan to buy 5 basketballs and 4 volleyballs. then How much does a basketball cost? How much does a volleyball cost?

Basketball (274 2-478 4) (3 2-5 4) 70 yuan. Volleyball (274-70 3) 2

32 yuan.

3 baskets + 2 rows = 274 yuan.

5 baskets + 4 rows = 478 yuan.

3 2 baskets + 2 2 rows = 274 2 = 548 yuan.

6 baskets 4 rows - 5 baskets 4 rows = 548 478

1 basket = 70 yuan.

Row: (274 70 3) 2=32 yuan.

The money for 3 volleyballs is 245-161=84, and if a volleyball is 84 3=28, then 3 basketballs are 161-2x28=105, then one basketball is 105 3=35

Satisfactory is selected.

Solution: Set a basketball x yuan, then a volleyball ** is (274-3x) 2 yuan, or (478-5x) 4 yuan, according to the topic, get.

274-3x）/2=（478-5x）/4

2（274-3x）=478-5x

548-6x=478-5x

6x+5x=478-548

x=-70x=70

274-3x70) 2=32 (yuan).

A: A basketball is 70 yuan, and a volleyball is 32 yuan.

The second and third days are 70% in total, the ratio is 9:5, if the total number of two days is 14, each serving is 5%, the second day is 45%, and the more than 240 tons is 15%, and the total is 240 tons. Children, think more if you have questions.

Set a total of x tons, the first day of the halo ton, the second day of transport (ton, the second day and the third day.

The ratio of the tonnage of the coal transported is 9:5, so the third day of transportation (multiply 5 9, after three days, calculate x.

x = 1600 tons.

In total, there are x tons of coal.

Then 30% of the total was shipped on the first day, and 70% x remained

The second day was 240 tons more than the first.

There is only 70% x-30% x-240 = 40% x-240 left, and the ratio of tons of coal transported on the second day to the third day is 9:5

Then on the third day, 5 (30%x+240) 9 is lucky, then there is. 5 (30%x+240) 9=40%x-240 gives x=1600

There are a total of 1,600 tons of coal.

Two years ago:

Three years later: Two times more before than three years later.

A: Xiao Li is 11 years old.

Explanation: 2 years ago, each parent was 2 years old, so the age was reduced by 4.

Xiao Li is also 2 years less than 2 years old, 2 times 9 times 18. Therefore, the age of the parents plus 14 years old is 9 times the age of Xiao Li this year.

After 3 years, each parent will be 3 years old, so 6 years will be added. It's 7 years younger, so add 7 to get 13.

Xiao Li is also 3 years older, 3 times that of 7 times that of Xiao Li is 21 years older, and his parents are 13 years older, using 21 minus 13 to get 8. Therefore, it can be concluded that the age of the parents is 8 years younger, which is equal to 7 times that of Xiao Li this year.

So 2 times the age of Xiao Li this year is exactly equal to 14 + 8 = 22, and Xiao Li is 11 years old this year.

Look at the age of the parents as a whole.

Let Xiao Li's age be x years old, and the age of his parents will be 9x.

x＋3）×7－7=9x＋3×2

7x＋14=9x＋6

2x = 8x = 4 (years).

A: Xiao Li is 4 years old this year.

Solution: Let's set: Two years ago, the age of my parents was 9x, and Xiao Li's age was x. Gotta :

9x+3+3）/（x+3）=7（x+3）-7（9x+6）/（x+3）=7x+21-7x=4

Let Xiao Li's age be x, and the parents' age and be y

y=9xy+3x2=7(x+3)-7

The solution is x=4y=36

Let the distance be s, then s is equal to ten minus s fifteen is equal to two, then s is sixty kilometers, when he rides ten kilometers per hour, then he rides sixty to ten equals six hours, and when he arrives at one o'clock in the afternoon, the departure time is seven o'clock in the morning! Now if he wants to arrive at twelve o'clock, he will have to ride for five hours, sixty to five equals twelve, and the speed is twelve kilometers per hour.

The small army should ride x kilometers per hour.

The difference between 1 p.m. and 11 a.m. is 2 hours.

If you arrive at 12 noon.

Difference of 1 hour.

2 hours is twice as much as 1 hour.

So 1 10-1 15 = 2 (1 x - 1 15) 2 x = 1 10 + 1 15 = 25 150

x=12

B's upper surface radius is half of A's lower surface radius.

Then the water volume of B is 1 (2x2x2)=1 8 of the volume of the cone, and the volume of water of A accounts for 1-1 8=7 8 of the volume of the container

A is 7 8 1 8 = 7 times that of B.

7 times let the cone height be radius r and the volume is v, then: v=1 2 r h v =1 2 (1 2r) (1 2h).

V-v =7 16 r h

v = 1 16 r h

v water A v water B = 7

As shown in the figure below, two identical conical containers each contain some water, and the depth of the water is half the height of the cone. Then the volume of water in container A is 7 times the volume of water in container B.