Petrol is 7 times heavy than kerosene and castrol Mobil is 18 times as heavy as Kerosene.

Ques - Petrol is 7 times heavy than kerosene and castrol Mobil is 18 times as heavy as Kerosene. What should be the ratio of petrol and Mobil in the new mixture to get the mixture which must be 11 times as heavy as kerosene ?

(a) 3 : 4

(b) 7 : 4

(c) 9 : 19

(d) 9 : 10

Solution - 

Let,

The weight of kerosene = x

Then,

The weight of Petrol = 7x

And,

THe weight of Castrol Mobil = 18x

Now,

Let,

The ratio of Petrol & Mobil = P : M

Then,

Total Mixture = P + M

Total Weight = (P + M) 11x  ( as it is 11 times as heavy as kersoene)

But,

Total weight = 7Px + 18Mx

(P + M) 11x = 7Px + 18Mx

11Px + 11Mx = 7Px + 18Mx

11Px - 7Px = 18Mx - 11Mx

4Px = 7Mx

4P = 7M

P/M = 7/4

Ratio of P : M = 7 : 4 

Thus,

The ratio of petrol and Mobil in the new mixture to get the mixture which must be 11 times as heavy as kerosene should be 7 : 4.

Hence,

The correct answer is option (b) 7 : 4.

Thank You