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4. Rohan covers x cm in one step. What distance will he cover (in cm) in 100 steps?

5. Swami reads 54 pages in a day. Find the number of pages he reads in n days.
6. If there are 50 mangoes in a box, how will you write the total number of mangoes in terms of the
number of boxes? (Use b for the number of boxes.)
7. Oranges are to be transferred from a larger box into smaller boxes. When a large box is emptied, the
oranges from it, fill two smaller boxes and still 10 oranges remain outside. If the number of oranges
in a small box is taken to be x, what is the number of oranges in the larger box?

8. Leena is Ruhi’s younger sister. Leena is 4 years younger than Ruhi. Can you write Leena’s age in
terms of Ruhi’s age? Take Ruhi’s age to be n years.

9. Ruhi’s mother made laddoos. She gave some laddoos to guests and family members; there were still 5
laddoos remain left. If the number of laddoos mother gave away is l, then how many laddoos did she make?

10. Rainwater harvesting is the collection and storage of rainwater rather than allowing it to run off. In a
village, there are 8 water tanks to collect rainwater. On a particular day, x litres of rainwater is collected
per tank. If 100 litres of water was already there in one of the tanks, what is the total amount of water
in the tanks on that day? Discuss the benefits of rainwater harvesting with the teacher.

Use of Variables in Common Rules

Let us now see how certain common rules in mathematics that we have already learnt are
expressed using variables.
Rules From Geometry
In geometry, we have already learnt about the perimeter of a rectangle and square. Let us use the
variables to represents the perimeter of a rectangle and square.
Perimeter of Rectangle

We know that, a rectangle is a 4-sided polygon with opposite sides equal and each angle is 90°.
And the perimeter of a rectangle is the sum of all four sides. In the adjacent D l C
figure, ABCD is a rectangle whose sides are AB, BC, CD, and AD. We have,
Perimeter of a rectangle = sum of all four sides b b
= length of the side AB + length of the side BC + length A l B
of the side CD + length of side DA
Since, in a rectangle opposite sides are equal. That is, the length of the side AB = the length of the
side CD and the length of the side AD = the length of the side BC
Perimeter of a rectangle = length of the side AB + length of the side BC + length of the side AB +
length of the side BC

= 2 × length of the side AB + 2 × length of the side BC

= 2 × (length of the side AB + length of the side BC)
Let us consider, length of the side AB = length of the side CD = l units (It is the length of the
rectangle), and length of the side BC = length of the side AD = b units (It is the breadth of the
rectangle). Therefore, the perimeter of the rectangle = 2(l + b) units

Here, l and b are the variables. They take the values independent of each other.
If we denote the perimeter of the rectangle by the variable p, then the rule for the perimeter of
a rectangle becomes 2l + 2b.

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