Question

Sonali bought one dozen notebooks for Rs.66. What did she pay for one notebook?
a). Rs.50
b). Rs.6.60
c). Rs.5.60
d). Rs.5.50

Answer 1

Hint: Given the cost of one dozen notebooks. We have to find the cost of one such notebook. We can use the unitary method here which gives the cost of a unit that is one quantity or we can simply divide the cost of one dozen notebooks by 12 because one dozen of notebooks means 12 notebooks.

Complete step-by-step solution:
We are given the cost of one dozen notebooks. We know that one dozen notebooks has 12 quantities.
So to find the cost of one such notebook we will divide the cost of one dozen notebooks by 12.
\[ = \dfrac{{66}}{{12}}\]
On dividing the number above we get,
\[ = 5.5\]
Thus this is the cost of one such notebook Rs.5.50
Thus option D is the correct option.

Note: Now how do we use the unitary method?
Cost of 12 notebooks = Rs.66
Cost of one notebook = ?
\[? = \dfrac{{66 \times 1}}{{12}}\]
This equals, \[ = 5.5\]
Note that when we are given the cost of many and need to find that of one we use divide operation. And in exactly the reverse case when we are given the cost of one and asked to find the cost of many we use multiplication operations.
Also note that there are various units of measurements like dozen, gross etc. we should use the multiple number according to the unit given.