Mr. Wang bought prizes for 15 excellent students at a total cost of 66 yuan, 4 yuan for each notebook and 5 yuan for each pen. How much did Mr. Wang buy

Mr. Wang bought prizes for 15 excellent students at a total cost of 66 yuan, 4 yuan for each notebook and 5 yuan for each pen. How much did Mr. Wang buy

Let the number of notebooks be x and the number of pens be y, x + y = 15, 4x + 5Y = 66

I often think of our teacher Liu and his kite

I think of Miss Liu and the kite

The school assigned the task of planting 220 trees according to the number of sixth grade students. There were 46 students in class one and 42 students in class two. How many trees should be planted in the two classes?

115 in class one, 105 in class two
Pro rata distribution
46÷(46+42)×220=115
42÷(46+420×220=105

There are 42 students in the first class and 340 trees in total; there are 38 students in the second class and 7 trees per person on average. How many trees per class and how many trees per person in the sixth grade?

Co planting trees
340 + 7 × 38 = 606 (trees)
Trees are planted in every class in Grade 6
606 △ 2 = 303 (trees)
Tree planting per capita
606 (42 + 38) = 7.575 (trees)

Two identical bottles contain the same amount of alcohol solution. The mass ratio of alcohol to water in one bottle is 4:1, and that in the other bottle is 4:1
Two identical bottles contain the same amount of alcohol solution. The mass ratio of alcohol to water in one bottle is 4:1, and the mass ratio of alcohol to water in the other bottle is 5:2. If two bottles of alcohol solution are mixed, what is the ratio of alcohol to water in the mixture

Mass ratio of alcohol to water in the mixture
(4+5)/(1+2)=9/3=3/1=3:1 .

There are several alcohol solutions with 36% alcohol content. After adding a certain amount of water, dilute them to a solution with 30% alcohol content. If the solution is diluted to 24%, how many times of the water added last time?

Assuming that the 36% alcohol solution is 100 g, then the alcohol content is 100 × 36% = 36 (g); 36 △ 30% - 100 = 20 (g); (36 △ 24% - 100-20) △ 20, = 30 △ 20, = 1.5 times; a: the amount of water added is 1.5 times of that added last time

An alcohol solution should be prepared in the laboratory. The mass ratio of alcohol to water is 1:5. (1) how many grams of water should be added to 600 grams of alcohol
(2) How many grams of alcohol should be added to 600 grams of water

The mass ratio of alcohol: water = 1:5, that is, the mass of water is 5 times that of alcohol

Mr. Wang plans to dilute 30 grams of 95% alcohol to 75%. How many kilograms of water should be added? (equation solution and formula)

Mass of alcohol: 30 * 95% = 28.5g
Total mass of alcohol and water after dilution: 28.5/75% = 38g
According to the law of conservation of mass
Mass of water: 38-30 = 8g = 0.008kg
Let the mass of water be X
（x+30）*75%=30*95%
The solution is x = 8g
Pay attention to unit conversion

There is a kilogram of 95% alcohol. How many grams of water should be added to make 75% alcohol according to the weight

W=1*95%/75%=1.27kg
Add water 0.27kg

In a certain alcohol solution, the ratio of pure alcohol to water is 1:2. The prepared alcohol solution is m kg, and water is needed______ Kilogram

∵ the ratio of pure alcohol to water in alcohol solution is 1:2 ∵ M. in kg alcohol solution, the mass of water is m × 23 = 2m3