Question

How many decimetres are there in 15 centimetres?
A. 150 dm
B. 1.5 dm
C. 0.15 dm
D. None of these

Answer 1

Hint: The SI unit of the system defines several units as standard as to be used in calculations. But the system of measurements is not just made up of one unit that is used. Several other units are used and they can be equally converted from one unit to another based on our need. Not all the units are used for the conversion.

Complete step by step answer:
The SI system of units describes the unit of length as a meter. It is defined as the length of the path travelled by light in a vacuum with a time of 1 second. It is represented by the letter ‘m’. Though meter is the SI standard for the calculation of the distance, it is not the only unit that is used in daily practice.
Apart from the unit, meter, the other units used are millimeter, centimeter, decimetre, decametre, hectometre, and kilometer. All these units differ from each other in the multiple of 10.
The number of centimeters in 1 decimetre is 10. So the number of decimetres in 1 centimeter will be 0.1 decimetres.
$1dm = 10cm$
$1cm = \dfrac{1}{{10}}dm = 0.1dm$
 So the number of decimetres in 15 centimeters will be 15 times 0.1 which will be 0.15 decimetres.
$15cm = \dfrac{1}{{10}} \times 15dm = 1.5dm$
We know the unit of decimetre is represented as ‘dm’
So the correct answer is B.

Note: Just as the meter, there are SI units defined for most of the major measurements like the distance, time, luminous intensity, weight, etc. All the units are set as the standards and the definitions of these measurements are clearly defined by the organizations.
Many units are more prevalent in some domains while the others are obsolete in others.