A 50 kg bag of rice costs Rs. 2500. What is the cost of 20kg rice?

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Hint: Start by finding out the rate or cost of each kg or 1 kg of rice. Later this value or rate can be used to find any quantity of rice, which can be computed by multiplying the rate and the desired quantity. All the units of different quantities must be written correctly.

Complete step by step solution:
Given, cost of 50 kg rice = 2500
Now, we know the cost of 50 kg rice is 2500, so let’s try to find out how much each kg or 1 kg of rice would cost.
Therefore, cost of 1 kg rice =$\dfrac{{2500}}{{50}} = 50/ - $
Now that we know the rate of rice i.e. Rs. 50 per kg. , let us compute the cost of 20 kg of rice as per the question.
The cost of 20 kg of rice will be found by the product of weight (kg) and rate per kg.
So, cost of 20 kg of rice =$20 \times 50 = 1000/ - $

Therefore, 20 kg of rice would have cost Rs. 1000.

Note: The methodology applied here is known as the Unitary method, In this method, we try to find the value of each unit in terms of other units and later that each unit value can be used for the vast scale of computation.
Such questions can also be asked the other way round, like how much rice in kg can be bought in Rs. 2000 when the 50 kg rice cost Rs. 2500.
Then the answer would be
Rice available for Rs. 2500 = 50
Rice available for Re 1 =$\dfrac{{50}}{{2500}}$
Then , rice available for Rs. 2000 =$\dfrac{{50}}{{2500}} \times 2000 = 40kg$