1、 There are two kinds of alcohol with 85% and 45% concentration. Now we need to prepare 400 grams of alcohol with 60% concentration

1、 There are two kinds of alcohol with 85% and 45% concentration. Now we need to prepare 400 grams of alcohol with 60% concentration

The best way to calculate this kind of problem is the cross method. First, calculate the mass ratio of 85% and 45% alcohol
（60-45）/（85-60）=3/5
It needs 85% alcohol, 400 × 3 / 8 = 150g
Need 45% alcohol 400 × 5 / 8 = 250 g

There are two kinds of wine with 75% and 45% concentration. Now we need to prepare 400 grams of wine with 65% alcohol. How much should we take from each of the two kinds of wine?

75% alcohol 800 / 3G,
45% wine 400 / 3G

When 10% alcohol and 85% alcohol are used to prepare 12 grams of 45% alcohol, how many grams of each alcohol are needed?

10%*a+85%*b=45%*12
a+b=12
10% alcohol 6.4
85% alcohol 5.6

When a bottle is filled with water, the total mass of water and bottle is 120g; when it is filled with alcohol, the total mass of alcohol and bottle is 100g (the density of alcohol is ρ = 0.8 × 103kg / m3). What is the mass of alcohol in the bottle?

Let the volume of the bottle be V, the mass of the bottle be m, ∵ ρ = MV, the total mass of water and bottle be m + ρ v = M1, i.e. m + 1g / cm3 × v = 120g & nbsp; ①, the total mass of alcohol and bottle be m + ρ V = m2, i.e. m + 0.8g/cm3 × v = 100g & nbsp; ②, the mass of alcohol be m alcohol = ρ V & nbsp; & nbsp