Question

One dozen of bananas cost \[Rs.18\]
How much will be paid for 60 bananas?
A. \[Rs.50\]
B. \[Rs.60\]
C. \[Rs.70\]
D. \[Rs.90\]

Answer 1

Hint: Here we use the concept of unitary method which helps us to find the value of multiple objects when we have the value of a single object by multiplying the number of objects with the value for one object.
* A dozen always contains \[12\] number of units.

Complete step-by-step answer:
We know cost of one dozen of bananas is \[Rs.18\]
Also we know one dozen bananas means \[12\] bananas
So, cost of \[12\] bananas is \[Rs.18\]
Using the unitary method to find the cost of one banana, divide the amount by \[12\] bananas.
Cost of one banana is \[Rs.\dfrac{{18}}{{12}}\]
Now using the unitary method to find cost of sixty bananas we multiply the cost of one banana to sixty
Cost of sixty bananas is \[Rs.\dfrac{{18}}{{12}} \times 60 = Rs.18 \times 5 = Rs.90\] { because \[12 \times 5 = 60\] so cancel out}

So, the correct answer is “Option D”.

Additional Information:
Unitary method is a method which helps us to find the value of a single unit when we are given the value of multiple units and find the value of multiple units when we are given the value of a single unit.
* If we are given the value of a single unit, we multiply the number of units to the value of a single unit and we get the value of multiple units.
* If we are given the value of multiple units then we divide the total value by the number of units to get the value of a single unit.

Note: Students are likely to make mistakes in questions which have units in different forms. Students are advised to use common conversions first to convert all the values in the same unit and then do calculations. Some conversions are:
\[
  1Kg = 1000 grams \\
  Rs.1 = 100 paisa \\
  1 Dozen = 12 units \\
    \\
 \]