29 pencils and 38 exercise books were awarded to a few students on average. As a result, there were 2 more pencils and 2 more exercise books. How many students won the prize

29 pencils and 38 exercise books were awarded to a few students on average. As a result, there were 2 more pencils and 2 more exercise books. How many students won the prize

27 pens and 36 books
One pen per person is not enough
Two pens per person is not enough
Three pens per person is OK
Up to 9 people! 3 pens and 4 books for each

(-1/42)/(1/6-2/7+2/3-3/14)
It's a process
Thank you

(-1/42)/(1/6-2/7+2/3-3/14)
=-1/42/(7/42-12/42+28/42-9/42)
=-1/42/(14/42)
=-1/14

The mass ratio of alcohol to water is 1:5. How many grams of water should be added to 600 grams of alcohol? How many grams of alcohol should be added to 600 grams of water?

Water = 600 × 5 = 3000 g
Alcohol = 600 △ 5 = 120 g

There are 160 grams of water with a density of 1 g / cm3 and 160 grams of alcohol with a density of 0.8 g / cm3. How many grams of disinfectant alcohol can be prepared with these 160 grams of water with a density of 0.84 g / cm3? (volume change during mixing is negligible)

Let m 1g of water and M 2G of alcohol be taken to make m g of disinfectant alcohol with density of ρ. The volume of water and alcohol will not change after mixing. M 1 ρ 1 + M 2 ρ 2 = M 1 + M 2 ρ, m 11 g / cm 3 + m 20.8 g / cm 3 = M 1 + m 20.84 g / cm 3 can make m 1 m2 = 516 ∵ M 2 > m 1. Therefore, when m 2 = 160 g of alcohol is taken, M 1 = 50 g of water can make disinfectant wine at most

What is the concentration of 80% alcohol a G after adding 10 g water?

∵ the concentration of 80% alcohol is 80% a in a gram, and the concentration after adding 10 grams of water is 80 AA + 10%

How much water does it take to change 10 liters of 50% alcohol solution into 20% alcohol solution

The percentage of alcohol is generally volume fraction, so the volume ratio of original alcohol and water is 1:1, that is, the volume of alcohol and water is 5 liters each
At 20%, the volume ratio of alcohol to water is 1:4, that is to say, adding three times the volume of water to alcohol is 15 liters

How many liters of water is needed to change 10 liters of 50% alcohol solution into 20% alcohol solution

15L

Add 30 liters of water into 20% alcohol solution, and the concentration will be 15%. How many liters of pure alcohol will be added, and the concentration will be 25%?

(1) When the concentration is 20%, water is alcohol: (1-20%) / 20% = 4, when the concentration is 15%, water is alcohol: (1-15%) / 15% = 173; 30 ／ (173-4) = 30 ／ 53 = 18 (L); 18 × 173 = 102 (L); when the concentration is 15%, the volume of alcohol is water: 15% ／ (1-15%) = 317, when the concentration is 25%

The volume ratio of bottle a and bottle B is 3:2, the alcohol ratio in bottle a and bottle B is 4:5, and the water ratio in bottle a and bottle B is 3:2

The volume ratio of bottle a and bottle B is 3:2, the ratio of alcohol in bottle a to that in bottle B is 4:5, and the ratio of water in bottle a to that in bottle B is 3:2. After mixing the two bottles, what is the ratio of alcohol to water?
A: 22:13
Analysis: (12 / 7 + 10 / 7): (9 / 7 + 4 / 7) = 22:13

The volume ratio of alcohol to water in bottle a is 3:1, and the volume ratio of alcohol to water in bottle B is 4:1

There is no notice here: whether the volume of a and B bottles is the same. Just do it as the same size
3÷（3＋1）＝3/4
4÷（4＋1）＝4/5
3/4＋4/5＝31/20
2－31/20＝9/20
31/20∶9/20＝31∶9………… Ratio of alcohol to water after mixing