Percentage

Total mixture = 60L
Milk : Water = 1 : 4
5x = 60
x = 12
Milk = 12L and Water = 48L
Milk percentage = 12/60 × 100 = 20%
And after adding only milk, the quantity of milk is becoming 15% which is not technically correct.
Because after adding a particular fluid, that's quantity should get increased.

Let the person's original salary be 100%.
Salary reduced by 20%, new salary = 80%
The difference ie., 20%, the salary should be increased by (20/80)×100 = 25%

Details

Let Rajesh had total amount = ₹ x.
Then, Money spent on buying the mobile = 20% of x = (20/100) × x = ₹ x/5
Now, remaining amount = x - (x/5) = 4x/5
Money spent on buying the DSLR = 15% of (4x/5)
= (15/100) × (4x/5)
= ₹ 3x/25
Then, he donated ₹ 160 in a trust and left with ₹ 1200.
∴ Total amount he had = Money spent on buying the mobile + Money spent on buying the DSLR + Money donated in a trust + Money left with him
⇒ x = (x/5) + (3x/25) + 160 + 1200
⇒ x - (x/5) - (3x/25) = 1360
⇒ (25x - 5x - 3x)/25 = 1360
⇒ 17x = 1360 x 25
⇒ x = (1360/17) × 25
⇒ x = 80 × 25
⇒ x = 2000
Thus, Total amount Rajesh had = ₹ 2000
Now, the amount he buy the DSLR for = ₹ 3x/25
= (3 x 2000)/25
= 3 x 80
= ₹ 240

Total passed students = x % of total students
total failed students = (100 - x)%
total girls passed = y % of x %
total boys passed = (100 - y)% of x % = (100 - y)/100 × x/100 of total students
Total failed boys = z% of (100 - x)%
total failed girls = (100 - z)% of (100 - x)% = [(100 - z)/100] × [(100 - x)/100] of total students
So the percentages of passed boys over failed girls = (100 - y)x × 100 / [(100 - z) (100 - x)]

Mamali scored 45% marks and failed by 18 marks
pass mark of the class = 45%of total mark + 18
Monali scored 54% marks and get 27 marks more than the passing marks
pass mark of the class = 54% of total mark - 27
total marks = x
Here passing marks equal. So,
45 % of x+ 18 = 54 % of x-27
18 + 27 = (54 — 45) % of x
45 = 9 % of x
x = 45×(100/9) = 500
Snigdha's mark = 75/100× 500 = 375

Amount of alcohol = 20% in 20 lltres
= 4 litres
Amount of water = 20 - 4 = 16 litres.
If 4 litres of water be mixed in it,
∴ Total quantity of new mixture = 24 litres
Percentage of alcohol in the new mixture = (4/24)×100
= 16($$\frac{2}{3}$$)%

Given, Pass percentage = 40%
Pass mark = 185 + 15 = 200
Let the maximum marks (100%) be x
Then, 40% of x = 200
⇒ (40/100) × x = 200
⇒ (4/10) × x = 200
⇒ x = (200 × 10) / 4
⇒ x = 500
∴ the maximum marks = 500

Let k be the amount he had invested originally.
Earning is 187, which is 22 % of k.
⇒(22/100)×k = 187
⇒ k = 187×(50/11)
⇒ k= 17×50
⇒ k= 850
Thus, the amount invested originally = ₹ 850