3 litres of water is added to 15 litres of a mixture of a 20% solution of alcohol in water. The strength of alcohol is now?

Let tax = Rs. 100 and Consumption = 100 units
Original expenditure = Rs. (100 x 100) = 10000
New expenditure = Rs. (120 x 80) = Rs. 9600
? Decreased in expenditure = (400 x 100)/1000 % = 4%

Reduction in consumption = (20/120) x 100% = 50/3%
? Reduction in consumption /Original consumption = (50/3) / 100 = 1/6 = 1 : 6

? (62% of N - 38% of N) =144
? 24% of N = 144
? N = (144 x 100)/24 = 600

Let third number be N
Then, first number = 70% of N = 7N/10 and,
Second number = 63% of N = 63N/100
Difference = 7N/10 - 63N/100 = 7N/100
? Required percentage = (7N/100) x (10/7N) x 100 % = 10%

? 72¹/₂% of N = 87
? {(145/2) x N} / 100 = 87
? N = (87 x 2 x 100) / 145 = 120

Let price = Rs. 100, sale = 100
Then sale value = Rs. (100 x 100) = Rs. 10000
New sale value = Rs. (70 x 120) = Rs. 8400
Decrease% = (1600/10000) x 100 % = 16%

Population after 2 years
=8000(1 + 10/100) (1 + 20/100)
= (8000 x 11/10 x 6/5) = 10560

? 540 = H(1 + 20/100)²
? H = (540 x 5/6 x 5/6) = 375 cm

Value of machine 2 years later = Rs. [ 4000 x {(1 - 10)/10)}²]
= Rs. (4000 x 9/10 x 9/10)
= Rs. 3240

Increase in 3 years over 100 = 100 x {1 + 7/(2 x 100)}³
= (100 x 207/200 x 207/200 x 207/200)
= (200 + 7)³ / 80000
= 88869743 / 80000 = 110.8718

Required increase % = (110.8 - 100)% = 10.8%