Percentage [प्रतिशत]–11 [SSC (CGL)-2015, TIER-II]

Question: Water tax is increased by 20%, but its consumption is decreased by 20%. Then, the increase or decrease in the expenditure of the money is [जल कर में 20% की वृद्धि हुई, लेकिन उसकी खपत 20% कम हुई. तो, धन के खर्च में वृद्धि या कमी कितनी हुई? [Ans. (d) 4% decrease] 

(a) No change (b) 5% decrease (c) 4% increase (d) 4% decrease 

Detailed Explanation: First Method: Let the expenditure be 100 units. If tax is increased by 20%, then the expenditure will also be increased by 20%, so it will be 100+20 = 120.

If consumption is decreased by 20%, then the expenditure will also be decreased 20%, so the resultant expenditure will be 120 - 20% of 120 = 120 -24 = 96

Therefore, the change = 96 - 100 = - 4   So, the decrease is 4%.  Ans

 

Second Method: When any quantity is changed by x% and y% successively, then the quantity is changed by

x + y + (xy)/100

So, the change is +20- 20+{(+20)×(-20)}/100 = - 4%.

Therefore, 4% decrease is the answer.