NCERT solution class 7 chapter 11 Perimeter and Area exercise 11.3 mathematics

EXERCISE 11.3

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Q 1, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 1:

Find the circumference of the circles with the following radius: (Takeπ)
(a) 14 cm (b) 28 mm (c) 21 cm

Answer:

(a) r = 14 cm
Circumference = 2πr  = 88 cm
(b) r = 28 mm
Circumference = 2πr  = 176 mm
(c) r = 21 cm
Circumference = 2πr  = 132 cm

Q 2, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 2:

Find the area of the following circles, given that:
(a) radius = 14 mm (Takeπ) (b) diameter = 49 m
(c) radius = 5 cm

Answer:

(a) r = 14 mm
Area = πr²  = 616 mm²
(b) d = 49 m
r =
Area = πr² == 1886.5 m²
(c) r = 5 cm
Area = πr² = = 78.57 cm²

Q 3, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 3:

If the circumference of a circular sheet is 154m, find its radius. Also find the area of
the sheet. (Takeπ)

Answer:

Circumference = 2πr =154 m

Area = πr² = 
=  = 1886.5 m²

Q 4, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 4:

A gardener wants to fence a circular garden of diameter 21 m. Find the length of the rope he needs to purchase, if he makes 2 rounds of fence. Also find the costs of the rope, if it cost Rs 4 per meter. (Takeπ)

Answer:

d = 21 m
r =
Circumference = 2πr == 66 m
Length of rope required for fencing = 2 × 66 m = 132 m
Cost of 1 m rope = Rs 4
Cost of 132 m rope = 4 × 132 = Rs 528

Q 5, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 5:

From a circular sheet of radius 4 cm, a circle of radius 3 cm is removed. Find the area of the remaining sheet. (Takeπ = 3.14)

Answer:

Outer radius of circular sheet = 4 cm
Inner radius of circular sheet = 3 cm
Remaining area = 3.14 × 4 × 4 − 3.14 × 3 × 3
= 50.24 − 28.26
= 21.98 cm²

Q 6, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 6:

Saima wants to put a lace on the edge of a circular table cover of diameter 1.5 m. Find the length of the lace required and also find its cost if one meter of the lace costs Rs 15.( Takeπ = 3.14)

Answer:

Circumference = 2πr

Cost of 1 m lace = Rs 15
Cost of 4.71 m lace = 4.71 × 15 = Rs 70.65

Q 7, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 7:

Find the perimeter of the adjoining figure, which is a semicircle including its diameter.

Answer:

Radius = 5 cm
Length of curved part = πr

= 15.71 cm
Total perimeter = Length of curved part + Length of diameter
= 15.71 + 10 = 25.71 cm

Q 8, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 8:

Find the cost of polishing a circular table-top of diameter 1.6 m, if the rate of polishing is Rs 15/m². (Take π = 3.14)

Answer:

Diameter = 1.6 m
Radius = 0.8 m
Area = 3.14 × 0.8 × 0.8
= 2.0096 m²
Cost for polishing 1 m² area = Rs 15
Cost for polishing 2.0096 m² area = 15 × 2.0096 = 30.14
Therefore, it will cost Rs 30.14 for polishing such circular table.

Q 9, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 9:

Shazli took a wire of length 44 cm and bent it into the shape of a circle. Find the radius of that circle. Also find its area. If the same wire is bent into the shape of a square, what will be the length of each of its sides? Which figure encloses more area, the circle or the square? (Takeπ)

Answer:

Circumference = 2πr = 44 cm

r = 7 cm
Area = πr² 
If the wire is bent into a square, then the length of each side would be =
Area of square = (11)² = 121 cm²
Therefore, circle encloses more area.

Q 10, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 10:

From a circular card sheet of radius 14 cm, two circles of radius 3.5 cm and a rectangle of length 3 cm and breadth 1 cm are removed (as shown in the following figure). Find the area of the remaining sheet. (Takeπ)

Answer:

Area of bigger circle == 616 cm²
Area of 2 small circles = 2 × πr²  = 77 cm²
Area of rectangle = Length × Breadth = 3 × 1 = 3 cm²
Remaining area of sheet = 616 − 77 − 3 = 536 cm²

Q 11, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Page No 224:

Question 11:

A circle of radius 2 cm is cut out from a square piece of an aluminium sheet of side 6 cm. What is the area of the left over aluminium sheet? (Take π = 3.14)

Answer:

Area of square-shaped sheet = (Side)² = (6)² = 36 cm²
Area of circle = 3.14 × 2 × 2 = 12.56 cm²
Remaining area of sheet = 36 − 12.56 = 23.44 cm²

Q 12, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 12:

The circumference of a circle is 31.4 cm. Find the radius and the area of the circle? (Take π = 3.14)

Answer:

Circumference = 2πr = 31.4 cm
2 × 3.14 × r = 31.4
r = 5 cm
Area = 3.14 × 5 × 5 = 78.50 cm²

Q 13, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 13:

A circular flower bed is surrounded by a path 4 m wide. The diameter of the flower bed is 66 m. What is the area of this path? (π = 3.14)

Answer:

Radius of flower bed = 33 m
Radius of flower bed and path together = 33 + 4 = 37 m
Area of flower bed and path together = 3.14 × 37 × 37 = 4298.66 m²
Area of flower bed = 3.14 × 33 × 33 = 3419.46 m²
Area of path = Area of flower bed and path together − Area of flower bed
= 4298.66 − 3419.46 = 879.20 m²

Q 14, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 14:

A circular flower garden has an area of 314 m². A sprinkler at the centre of the garden can cover an area that has a radius of 12 m. Will the sprinkler water the entire garden? (Take π = 3.14)

Answer:

Area = πr² = 314 m²
3.14 × r² = 314
r² = 100
r = 10 m
Yes, the sprinkler will water the whole garden.

Q 15, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 15:

Find the circumference of the inner and the outer circles, shown in the adjoining figure? (Take π = 3.14)

Answer:

Radius of outer circle = 19 m
Circumference = 2πr = 2 × 3.14 × 19 = 119.32 m
Radius of inner circle = 19 − 10 = 9 m
Circumference = 2πr = 2 × 3.14 × 9 = 56.52 m

Q 16, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 16:

How many times a wheel of radius 28 cm must rotate to go 352 m?
(Take π  )

Answer:

r = 28 cm
Circumference = 2πr = = 176 cm
Number of rotations =
Therefore, it will rotate 200 times.

Q 17, Ex 11.3 - Perimeter and Area - Chapter 11 - Maths Class 7th - NCERT

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Question 17:

The minute hand of a circular clock is 15 cm long. How far does the tip of the minute hand move in 1 hour. (Take π = 3.14)

Answer:

Distance travelled by the tip of minute hand = Circumference of the clock
= 2πr = 2 × 3.14 × 15
= 94.2 cm