Question

If one apple is 20 rupees then how many apples will be in 180 rupees?

Answer 1

Hint: A bigger quantity is divided by smaller to get a number of (how many) items.
For example: If the cost of a pen is 5 rupees and you have 10 rupees, then the total number of pens you can buy is 2 (two pens). It is simply done by calculating division $10 \div 5$ .

Complete step by step solution:
Step 1
  The cost of one apple = 20 rupees (given)
Step 2
        Total rupees given = 180 rupees (given)
Step 3
    Number of apples $ = \dfrac{{{\rm{total rupees given (in rupees) }}}}{{{\rm{cost of one apple (in rupees)}}}}$
                                     \[ = \dfrac{{180{\rm{ rupees}}}}{{20{\rm{ rupees}}}}\]
                                     \[ = \dfrac{{18{0}{\rm{ }}{{{\rm{rupees}}}}}}{{2{0}{\rm{ }}{{{\rm{rupees}}}}}}\] ( same units get cancelled on division)
                                     $ = \dfrac{{18}}{2}$ ( 2$ \times $9 = 18)
                                     = 9 apples

There are 9 apples for 180 rupees when the cost of one apple is 20 rupees.

Note:
Two quantities are divided only when their units are the same. For example, 1 kg cannot be divided by 50 g. Kilogram should be converted into grams or gram should be in kilograms.
 Kilograms is a bigger unit than grams.
To convert kilogram into gram, it is multiplied by 1000 and to convert grams into kilograms, it is divided by 1000. Some useful interconversion of units are as follows:
$1kg = 1000g$
$1g = 1000mg$
\[1g = \dfrac{1}{{1000}}kg\]
$1mg = \dfrac{1}{{1000}}g$
$1mg = \dfrac{1}{{1000 \times 1000}}kg$
1 rupees = 100 paisa
1 paisa $ = \dfrac{1}{{100}}{\rm{rupees}}$