water tax is increased by 20 but its consumption decreased then..., Percentage, General Mathematics

Question:Water tax is increased by `20%` but its consumption is decreased by `20%`. Then, the increase of decrease in the expenditure of the money is :

A No change 
B `5%` decrease 
C `4%` increase 
D `4%` decrease

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+ AnswerD

+ ExplanationLet original consumption `= 100` units &

Tax `= Rs. 100` per unit.

Then original expenditure `= Rs. 100 xx 100` 

New expenditure `= 80 xx 120 = Rs. 9600`,

Decrease in expenditure `= ((400)/(100 xx 100) xx 100)%`

`= 4%`

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