Two solution of 90% and 97% purity and mixed resulting in 21 liters of mixture of 94% purity. How much is the quantity of the first solution in the resulting mixture?

Method 1 to solve the equation.
Let us assume Cost Price (C.P) of 1 liter milk be Y rupees.
According to question,
Selling Price (S.P) of 1 liter of mixture Y rupees. (Selling price should be same as Cost price)
Profit = 50/3 %
Let us assume Cost price of 1 Liter of Mixture of Water and Milk = C
Cost price of 1 Liter of Mixture of Water and Milk = Selling price of Mixture - Profit
C = Y - C x 50/3%
? C = Y - C x 50/3x100
? C = Y - C x 1/3x2
? C = Y - C/6
? Y = C + C/6
? Y = (6C + C)/6
? Y = (6C + C)/6
? Y = 7C/6
? C = 6Y/7
Since in Y rupees we will get 1 liter milk.
Hence in 1 rupees we will get 1/Y liter milk.
Hence in 6Y/7 rupees we will get 1 x 6Y/7 x Y liter milk.
Hence in 6Y/7 rupees we will get 6/7 liter milk.
We need 1 liter mixture of milk and water for sold on the same price, we need to mix the water.
So water quantity in mixture = 1 - 6/7 = 1/7

Ratio of Milk and water in mixture = quantity of Milk in Mixture/quantity of Water in Mixture
Ratio of Milk and water in mixture = 6/7 / 1/7
Ratio of Milk and water in mixture = 6 x 7 / 7
Ratio of Milk and water in mixture = 6 / 1
Ratio of Milk and water in mixture = 6 : 1

Method 2 to solve the question.
Let the original amount of milk be 1 liter and the cost price is 1 rupees per liter.
Cost price of milk = 1 rupees.
Selling price of Mixture = 1 rupees.
When the milk is mix with x liters of water milk remaining is 1- x.
Let us assume the cost price of milk in mixture is Y and given that the Sold Price is 1.
we should use the Profit formula in algebra,
Y + Y x 50/3 % = 1
Y + Y x 50/3 x 100 = 1
Y + Y x /3 x 2 = 1
7Y/6 = 1
Y = 6/7
Y = 6/7 is the cost price of Mixture for 1 liter.
Since water is free so there is not cost of water in mixture. So price of milk is 6/7 rs in mixture.
Since as per question,
In 1 rupees we will get 1 liter of milk.
hence in 6/7 rupees we will get 1 x 6/7 = 6/7 liter of milk.
Now we have to make 1 liter of mixture with water and milk.
quantity of Water + Quantity of Milk = 1 liter
quantity of Water + 6/7 = 1
quantity of Water = 1 - 6/7 = (7 - 6)/7
quantity of Water = 1/7
Ratio of milk and Water = Quantity of Milk / quantity of Water
Ratio of milk and Water = (6/7) / (1/7)
Ratio of milk and Water = (6/7) x (7/1)
Ratio of milk and Water = 6 x 7/ 7 x 1
Ratio of milk and Water = 6 :1

Let us assume the number of boys = B and number of girls = G.
According to question,
B + G = 30
Lets us assume total weight of boys = W1 and total weight of girls = W2
average weight of boys = total weight of boys/number of boys
total weight of boys/number of boys = 20
W1/B = 20
W1 = 20B

average weight of girls = total weight of girls/number of girls
25 = W2/G
W2 = 25G

Data is not sufficient to solve the equation.
since we do not know either the average weight of the whole class or the ratio of no. of boys to girls.

Let us assume the ratio factor is x.
According to question,
Quantity of milk = 4x liters and Quantity of Water = x liters.
According to question,
4x + x = 45
? 5x = 45
? x = 9
Quantity of milk = 4x = 9 x 4 = 36 liters
Quantity of water = x = 9 liters
Let y liters of water be added to make the ratio 3:2
Then,
36/(9 + y) = 3/2
? 72 = 27 + 3y
? y = 15 liters
If you add 15 liters of water, the ratio will become 3:2.

The difference counts only due to 40% of the profit which was distributed according to their investments.

Let total profit = R.
40% of R is distributed in the ratio, 125000 : 85000 = 25 : 17

Share of 1st partner = 40% of R x25/(25 + 17)
= 40% of 25R/42 = (40/100) x (25R/42) = 5R/21

Share of 2nd partner
= 40% of 17R/42 = (40/100) x (17R/42) = 17R/105

Now according to the question
5R/21 - 17R/105 = 600
? R(25 - 17)/105 = 600
? R = (600 x 105)/8
= ? 7875

A's share : B's share : C's share
= [16000 x 3 + (16000 - 5000) x 9] : [12000 x 3 + (12000 + 5000) x 9] : (21000 x 6)
= (16 x 3 + 11 x 9) : (12 x 3 + 17 x 9) : (21 x 6)
= 147 : 189 : 126
= 7 : 9 : 6

Hence, B's share exceeds C's share by = {13200/(7 + 9 + 6)} x (9 - 6)
= (13200 x 3)/22
= ? 1800

Using Alligation rule,
(Quantity of cheaper tea) / (Quantity of dearer tea) = (d - m) / (m - c) = 7/3
Therefore, they must be mixed in the ratio of 7 : 3.

Cost price of the mixture = 15 × (100 / 180) = Rs. 25/3 per kg
(Quantity of rice @ Rs. 8 per kg) / (Quantity of rice @ Rs.10 per kg) = (5 / 3) / (1/3) = 1/5
Quantity of rice @ Rs. 10 per kg = 25 × (1/ 5) = 5 kgs.

He should mix 30% and 50% in the ratio 5 : 15 or 1 : 3.
( 30% Solution ) / (50% Solution) = 1 / 3 or 1 : 3

According to figure we can find that the ration would be 1 : 7.
Quantity sold at 10% profit = 1 / (1 + 7)× 160 = 20 kgs.
Quantity sold at 6% loss = (160 ? 20) = 140 kgs.

Let the remainder stock be sold at P% profit.
(P - 20) / 30 = ((1 / 4) / (3 / 4))
or (P ? 20) = 30 × (1 / 3)
or P = 20 + 10
P = 30% profit.