Ask everybody a mathematics application problem, come person, thief Oxygen 21%, nitrogen 78%, others 1%, write their comparison and simplification

Ask everybody a mathematics application problem, come person, thief Oxygen 21%, nitrogen 78%, others 1%, write their comparison and simplification

Oxygen: nitrogen: others = 21%: 78%: 1% = 21:78:1

If a rope is bent three times to measure a classmate's height, the rope length is 0.2 meters above the top of the head; if it is bent four times, the rope length is 0.2 meters above the top of the head. How many meters are the rope length and the classmate's height?
(it's better to set up the formula, if it's not possible, set up the equation, but write the process of the equation ~)

First, let the height be x meters. According to the meaning of the question, we get 3 (x + 0.2) = 4 (x-0.2), that is, 3x + 0.6 = 4x-0.8. The solution is that x = 1.4 is the height. Then we substitute x = 1.4 into 3 (x + 0.2) or 4 (x-0.2) to get the rope length of 4.8 meters

Sixth grade mathematics summer homework
1: The fruit shop shipped 25 baskets of apples and 60 baskets of pears, weighing 2645 kg. It is known that each basket of apples is 20 g lighter than each basket of pears, so how many kg do each basket of pears and apples weigh?
2: How many days will Party A and Party B complete the project in cooperation, one in ten days?
3: To build a section of highway, one fourth of the total length will be built on the first day, and ten percent on the second day. There are still 4.2 kilometers left to be built. How long is this highway?
4: A pile of 10 tons of coal, the first week to use two fifths of the tons, the second week to use the remaining 25%, the second week to use how many tons of coal?
5: Xiaofang read 45 pages in two days. On the first day, she read one fifth of the whole book. On the second day, she read 25 pages

1. Let the solution of the equation of one variable be x kg for each basket of pears (don't forget to write, or you'll lose a cent) 25 (x-20) + 60x = 264525x-500 + 60x = 264525x + 60x = 2645 + 50085x = 3145x = 3737-20 = 17 (kg) a: each basket of pears weighs 37 kg and apples 17 kg