Question

If half a litre of milk cost Rs. 22, How much will 7 litre costs?

Answer 1

Hint: We will first convert litres into millilitres using the conversion formula given as $ 1l=1000ml $ . So, we will convert half litre and 7 litres into millilitre. On doing this we will get 500ml and 7000ml. Then we will again apply a unitary method to find the cost of 7000ml. We will get as $ \begin{align}
  & 500ml=Rs.22 \\
 & 7000ml=? \\
\end{align} $ . On solving we will get the answer.

Complete step-by-step answer:
Here, we will convert litre into millilitre using the conversion formula given as $ 1l=1000ml $
So, we will convert half litre and 7 litres into millilitre using the rule. We get for half litre by applying unitary method as
 $ \begin{align}
  & 1l=1000ml \\
 & \dfrac{1}{2}l=? \\
\end{align} $
On further solving, we get as
 $ \dfrac{1}{2}\times 1000=500ml $ ……………………(1)
Similarly, we will apply a unitary method for 7litres. We get as
 $ \begin{align}
  & 1l=1000ml \\
 & 7l=? \\
\end{align} $
On further solving, we get as
 $ 7\times 1000=7000ml $ ………………..(2)
Now, we can say that if 500ml costs Rs. 22 then how much will 7000ml costs. So, on applying unitary method, we can write it as
 $ \begin{align}
  & 500ml=Rs.22 \\
 & 7000ml=? \\
\end{align} $
On solving, we get as
 $ =\dfrac{7000\times 22}{500} $
We will get after further simplification,
 $ =\dfrac{70\times 22}{5}=\dfrac{1540}{5} $
 $ =Rs.308 $
Thus, we can say that 7litres cost Rs. 308.

Note: Another approach is directly applying unitary method i.e. given as
 $ \begin{align}
  & 0.5l=Rs.22 \\
 & 7l=? \\
\end{align} $
On further solving we will get as $ \dfrac{7\times 22}{0.5}=Rs.308 $ . This is only one step answer and is easy to calculate. So, we do not need to convert litres to millilitres and then solve it as it is a long method.