if the price of the petrol increases by 25%,Santosh intends to spend only 15% more on petrol, how much % should he reduce the quantity of petrol that he buys?​

Suppose Santosh buys quantity of gasoline today =x
Let today's price of gasoline be equal to=y

Santosh spends on gasoline today =xy

The new price of gasoline is
(increase by 25%)
=
1.25×y

Santosh wants to spend only 15% more,
∴
he wants to spend=1.15 ×xy

Quantity he buys at new rate=
1.15 ×xy
=
1.25×y

1.15x

1.25

Reduction in quantity of purchase=

x- (1.15x/1.25) = 0.10x / 1.25

% Reduction in quantity of purchase of gasoline
=
0.10x

1.25
×100 =
x

0.10
×100
1.25

=
8%

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