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We shall denote Ruhi’s stamps by the letter x. Here, x is a variable, which can take any value 1, 2,
3, 4, ... ,10, ... ,20, ... , 30, ... and so on.

Using x, we can write Rohan's stamps as x + 5.
This expression (x + 5) is read as ‘x plus five’. It means 5 added to x.
If x is 2, then (x + 5) will be 7 and if x is 10, then (x + 5) will be 15 and so on.

We use a letter to show such an unknown quantity as we talked in the above situations and calculate
as we do in arithmetic with mathematical operations.
In the same way for another situation, let us consider you have y number of marbles. After giving
7 marbles to your younger brother. How many marbles were left with you?

The number of marbles left = Number of marbles you have –7
Since, we considered initially that you have y marbles. Therefore, the number of marbles left after
giving 7 marbles to your brother will be y – 7.

It is clear from the above situations that to represent any mathematical situation using variables
and numbers, we just put signs of mathematical operations on them.

The expression (x + 5) and (y – 7) cannot be simplified further.

Do not confuse (x + 5) with 5x, they are different.
In 5x, x is multiplied by 5. In (x + 5), 5 is added to x.
Example 2: NCC cadets are marching in a parade on Annual day and there are 6 cadets in a row.
What is the rule which gives the number of cadets, in the n number of rows?

Solution: Let n be the number of cadets marching in the parade.
Since, there are 6 × 1 cadets in a row.

Therefore, there will be 6 × 2 cadets in second row.
And there will be 6 × 3 cadets in third row.

Since, there are n number of rows in the parade,
So, the number of cadets, will be given by the rule 6 × n.

Thus, the number of cadets in n number of rows marching in the parade = 6 × n = 6n.
Example 3: Uma is drawing a beautiful Rangoli pattern on Ganesh Chaturthi by joining dots through
lines. She has 9 dots in a row. How many dots will her Rangoli have for x rows? How many dots are
there if there are 8 rows and 10 rows?
Solution: We know that each row of rangoli has 9 dots.

Let the number of rows be x.
Therefore, total number of dots in x rows = Number of dots in each row × number of rows

Therefore, the total number of dots in x rows will be 9x.
If the number of rows is x = 8.

Then, the number of dots for 8 rows will be 9 × 8 = 72.
If the number of rows is x = 10.

Then, the number of dots for 10 rows will be 9 × 10 = 90.

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