Question

A boat can travel 36 kms on 4 litres of petrol. How much petrol will it need to go 180 kms?

Answer 1

Hint: In such a type of question we use the UNITARY method. In this method we first find the value for a single unit. Here we find kilometres travelled by the boat in one litre of petrol. After that we find necessary values by multiplying the single unit value. So we have to multiply the total distance covered that is 180 kms by per kilometre consumption of petrol.

Complete step-by-step answer:
From question we can find the following information
A boat can travel 36 kms on 4 litres of petrol
So, for one litre of petrol the boat can travel $\dfrac{36}{4}=9$ kilometres
Here we divide the kilometres travelled by the amount of petrol used.
Hence, we can say that
For 9 kilometre the boat requires 1 litre of petrol
So, for 1 kilometre the boat requires $\dfrac{1}{9}$litres of petrol
We have to find out how much petrol is required for 180 kms.
So here direct variation is in between consumption of petrol and distance travelled by the boat.
Hence, for 180 kms the boat requires $\dfrac{1}{9}(180)=20$litres of petrol.
Here we multiply consumption of petrol per kilometre with a total distance that is 180 kms.
Hence, 20 litres of petrol will need to go 180 kms.

Note: the above question is based on direct variation that is increased in one quantity causes increase in the other. Here we see that distance covered by the boat is in direct variation with the consumption of petrol. With more petrol consumption more distance is travelled.