Two ninths of a number is one half. What is nine seventh of the number

Two ninths of a number is one half. What is nine seventh of the number

Hello:
1/2÷2/9×9/7
=1/2×9/2×9/7
=81 / 28

One half of a number is less than two-thirds of this number. How much is this number? There must be a formula

Let this number be X
Then 2x / 3-x / 2 = 18
x/6=18
x=108

Two thirds of a number is more than one-half of the number. What's the number

22÷（2/3-1/2）=22×6=132

When we buy drinks, we have 52 people. We buy four boxes, one for each person. When we buy one box, we get one free. How many boxes are there in each box? How to calculate? Please explain the basic principle and formula?
Why (52-4) △ 4 = 12? Please explain the basic principle. Thank you

If you buy one box, you get one box free. If you buy four boxes, you get four boxes free. If you add four boxes to four boxes, you will get 52 boxes. So 52 minus four is the whole four boxes. Dividing by four is the number of boxes in each box

1 by 1 / 3 + 2 by 1 / 4 + 3 by 1 / 5 + 9 times 1 / 11

1/(1*3)=1/2*(1-1/3)1/(2*4)=1/2*(1/2-1/4).1/(9*11)=1/2*(1/9-1/11)1/(1*3)+1/(2*4)+...+1/(9*11)=1/2*(1-1/3+1/2-1/4+...+1/6-1/8+1/9-1/11)=1/2*(1+1/2-1/8-1/11)=1/2*113/88=113/176

On the map with a scale of 1:6000000, the distance between a and B is 25cm. At 8:30 a.m., a plane flies from a to B, and the distance between a and B is 25cm
It arrived at 10:30 a.m. how many kilometers does the plane fly per hour?

1: On the 6000000 representative map, 1cm corresponds to 60km
Therefore, 25cm on the map is equivalent to 25 * 60 = 1500km
It's two hours from 8:30 to 10:30, so
The speed is 1500 / 2 = 750km / h

(1 + 3 + 5 + 7 +. + 2001 + 2003 + 2005) - (2 + 4 + 6 +. + 2000 + 2002 + 2004)

(1 + 3 + 5 + 7 +. + 2001 + 2003 + 2005) - (2 + 4 + 6 +. + 2000 + 2002 + 2004)
=1+（3-2）+（5-4）+（7-6）+… +（2005-2004）
=1003

At the same time, the two trains run from a and B to each other. Car C is 150 km and car D is 120 km. The distance between the two places is 300 km. The two trains meet in a few hours

300÷（150+120）
＝300÷270
＝10/9
=1 and 1 / 9 (hours)

(8-2x)(6-2x)=24

(8-2x)(6-2x)=2448-16x-12x+4x²=24
4x²-28x+24=0
x²-7x+6=0
（x-1）（x-6）=0
x1=1.x2=6

A. The distance between the two places is 360 kilometers. A and B start from both places at the same time and run in opposite directions. They meet three hours later. It is known that the speed ratio of a to B is 7:5, so we can find the speed of B

360 △ 3 = 120 (km), the speed of car B accounts for a few parts of the sum of the speed of car a and B: 5 △ 7 + 5 = 512120 × 512 = 50 (km); answer: the speed of car B is 50 km