Question

If $10$ pens cost $Rs.60$. What is the cost of $13$ such pens?

Answer 1

Hint: We will make use of the unitary method to solve the given problem. Which is to convert the given quantities into one term and then solve according to them like from the given we have two quantities, cost of the pens in rupees and quantity of the pens. Hence, we will convert them as pen quantities to solve the given question.

Complete step by step answer:
Given that ten pens cost is rupees sixty, which can be represented mathematically as $10P = 60rs$ where P is the quantity of the pen and then equals with the rupees given.
Hence divide both values with the number $10$ then we will get the quantity of the pen as one and also its rupees respectively.
Hence, we have $\dfrac{{10}}{{10}}P = \dfrac{{60}}{{10}}rs$
$ \Rightarrow 1P = 6rs$
Thus, we have one pen rupee as six.
Now multiply with the number $13$, because to obtain the cost of $13$ such pens. Hence, we get $13P = 13 \times 6 \Rightarrow 78$
Therefore $Rs.78$ is the cost of $13$ such pens.

Note:
The operations which we used to solve the problem are multiplication and division operations.
Since multiplicand refers to the number multiplied. Also, a multiplier refers to the number that multiplies the first number. Have a look at an example; while multiplying $5 \times 7$the number $5$ is called the multiplicand and the number $7$is called the multiplier. Like $13P = 13 \times 6 \Rightarrow 78$
The process of the inverse of the multiplication method is called division. Like $x \times y = z$is multiplication thus the division sees as $x = \dfrac{z}{y}$. Like $\dfrac{{10}}{{10}}P = \dfrac{{60}}{{10}}rs \Rightarrow 1P = 6rs$
And the other two operations are addition and subtraction.
In mathematics, these four operations are the basis for it.