RBSE Solutions Class 5 Maths Chapter 14 Perimeter and Area More Ques

Page No. 72

Question 1. Nirmal's mathematics book has questions to find the perimeter of some shapes: Can you find out the perimeter of the above three shapes?
Answer: No, we cannot find the perimeter of shapes (b) and (c). This is because only closed shapes have a perimeter, and shapes (b) and (c) are not closed. Shapes like (b) and (c) are known as open shapes, which do not enclose an area completely.
In simple words: You can only find the perimeter of shapes that are fully closed. Shapes (b) and (c) are open, so their perimeter cannot be measured.

🎯 Exam Tip: Remember that perimeter is the total distance around the boundary of a shape, which only makes sense for shapes that are completely closed.

Page No. 72

Question 1. Some shapes are given below: Find out the perimeter of these shapes.
Answer:
(a) This shape is a triangle with all sides equal (a regular shape).
Perimeter = Number of sides \( \times \) Length of a side
Perimeter \( = 3 \times 10 \text{ cm} = 30 \text{ cm} \).
(b) This shape is a square with all sides equal.
Perimeter \( = 4 \times 12 \text{ cm} = 48 \text{ cm} \).
(c) This shape is a pentagon with all sides equal.
Perimeter \( = 5 \times 7 \text{ cm} = 35 \text{ cm} \).
In simple words: To find the perimeter of these shapes, you add up the lengths of all their sides. For regular shapes, you can just multiply the number of sides by the length of one side.

🎯 Exam Tip: Always check if a shape is regular (all sides equal) or irregular before applying a formula; for irregular shapes, you must add each side individually.

Page No. 73

Try these

Question 1. Think, is rectangle a regular shape? If you want to find a formula for the perimeter of a rectangle. What will you do?
Answer: No, a rectangle is not a regular shape. This is because all its sides do not have the same measurement; only opposite sides are equal. To find a formula for the perimeter of a rectangle, you would add its length twice and its breadth (or width) twice.
Perimeter \( = 2 \times \text{length} + 2 \times \text{breadth} \).
In simple words: A rectangle is not a regular shape because its sides are not all the same length. Its perimeter is found by adding two lengths and two breadths together.

🎯 Exam Tip: Remember that regular shapes have all sides and all angles equal; a rectangle only has equal opposite sides and 90-degree angles, making it an irregular shape.

Page No. 75

Question 1. Some shapes are given below on grid paper. Find the area of these.
Answer:
(i) The shape is a rectangle.
If each small square on the grid paper has a side of 1 cm, then:
Length of the rectangle \( = 5 \text{ cm} \)
Width of the rectangle \( = 2 \text{ cm} \)
The number of squares covered by rectangle ABCD \( = 10 \).
Therefore, the area of rectangle ABCD \( = 10 \text{ square cm} \).
The rule for finding the area of a rectangle is: Length \( \times \) Width \( = \) Area.
So, \( 5 \text{ cm} \times 2 \text{ cm} = 10 \text{ square cm} \).
(iii) The shape is a rectangle.
Length of the rectangle \( = 7 \text{ cm} \)
Width of the rectangle \( = 3 \text{ cm} \)
The number of squares covered by rectangle ABCD \( = 21 \).
Therefore, the area \( = 21 \text{ square cm} \).
In simple words: To find the area of a shape on grid paper, count how many small squares it covers. For a rectangle, you can also multiply its length by its width to get the area.

🎯 Exam Tip: Always count the full squares first and then estimate or combine partial squares when finding the area on a grid. For perfect rectangles, the length times width formula is quicker.