50L

20 = 30

20(2) = 40

20/2 = 10

40+10 = 50

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Answer:

Answer 30 litres of alcohol to be added to make the mixture 80% from 65%

Step-by-step explanation:

How many liters of alcohol must be added to 40 liters of a mixture which is 65% alcohol to obtain a mixture which is 80% alcohol?

65% is 65/100 = 0.65

80% is 80/100 = 0.80

Let x litres of alcohol to be added to 40 litre of mixture

Therefore

0.65 (40 L ) + x = 0.80 (40 L + x)

40 × 0.65 + x = 40 × 0.80 + 0.80x

26 + x = 32 + 0.80x

x - 0.80x = 32 - 26

0.20x = 6

x = 6 / 0.20

x = 30 litres