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In 2000 the rate of milk per liter was Rs. 15. In 2010, the rate of milk was Rs. 35 per liter. By what percentage of the price grew up?


Answer
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Hint: Start by taking the rate of milk in the year 2000 as some variable, similarly the rate of milk for the year 2010. Then compute the increase or change in the rate of milk over the years. Use the percentage formula to find out the percentage increase in the rate of milk.

Complete step by step solution:
Given,
The rate of milk in the year $2000 = Rs. 15/-$
Rate of milk in the year $2010 = Rs. 35/-$
Let, the rate of milk in the year 2000 = ${R_1}$
Then, the rate of milk in the year 2010 = ${R_2}$
Since in the question it says an increase in the rate of milk, We will subtract the rate in the year 2000 from the rate in 2010.
Change in the rate of milk = rate of milk in 2010 – rate of milk in 2000
So, the change in the rate of milk = ${R_2} - {R_1} = 35 - 15 = 20$
We know,
\[{\text{Percentage change = }}\dfrac{{{\text{Change in quantity}}}}{{{\text{Original or Initial quantity}}}} \times 100\]
\[ \Rightarrow {\text{Percentage increase = }}\dfrac{{{R_2} - {R_1}}}{{{R_1}}} \times 100\]
Substituting all the values known , we get
$
   \Rightarrow {\text{Percentage increase = }}\dfrac{{20}}{{15}} \times 100 = \dfrac{{400}}{3} \\
  \therefore {\text{Percentage increase = 133}}{\text{.33\% }} \\
$
Therefore , There was a 133.33% increase in the rate of milk over the span of 10 years or a decade.

Note: Students must be well aware of all the terms of profit and loss, how to find the percentage of any quantity in order to solve such similar questions. Similar problems can be asked involving determining the cost of milk in the next 5 years. Here we get the positive value in the difference of rate which shows the percentage increment, on the other hand, if the difference is negative then that shows the percentage decrease of milk rate.