Question

A postage stamp is 12 mm in breadth and 20 mm in length. Find the area of stamp in sq. cm.
(a) 0.24
(b) 240
(c) 24
(d) 2.4

Answer 1

Hint: This question mainly focuses on conversion of units as the dimensions of the stamp are given in mm and we are asked to find the are of the stamp in sq. cm. There are two approaches to solve this question. We can either convert the dimensions before finding the area of the stamp or first find the area and then convert the units. As two dimensions, length and breadth are given, we can deduce that the shape of the stamp is rectangular and the area of a rectangle is given by the product of its length and its breadth. We will use the former approach as it is relatively easier than the later.

Complete step-by-step answer:
The figure of the stamp is as follows:

It is given that the length of the stamp is 20 mm and the breadth is 12 mm.
We know that the 1 cm = 10 mm.
Thus, 1 mm = 0.1 cm
 $ \Rightarrow $ 20 mm = 0.1 (20) cm
 $ \Rightarrow $ 20 mm = 2 cm
 $ \Rightarrow $ 12 mm = 0.1 (12) cm
 $ \Rightarrow $ 12 mm = 1.2 cm
So, the dimensions in cm are length = 2 cm and breadth = 1.2 cm.
The area of a rectangle is given as the product of its length and breadth.
Thus, area of rectangular postage stamp = 2 X 1.2
Therefore, area = 2.4 sq cm.
So, the correct answer is “Option D”.

Note: Students can opt the second method too in which we will first find the area in sq. mm and then convert the sq. mm into sq. cm. To execute this conversion, we need to multiply the area by $ {{0.1}^{2}} $ as the mm has a power of 2. It is advisable to be well versed with the units and their conversions.