Question

1. Find the circumference of the circles whose diameters are:
(a) 42 cm
(b) 9.1 cm
(c) 105 cm​

Answer 1

Answer:

put the formula 2πr

and the value of π= 22/7

then put 2×22/7×42

so answer will be 2×22×6

Answer 2

(a) 42cm.

Given diameter of the circle :

• 42cm.

Since, radius is ½ of the diameter

So, radius will be half of 42cm or, 21cm.

→ Circumstance of a circle is given by : → 2πr

• Taking ‘π’ as $\sf \frac{22}{7}$
• r (radius) = 21cm

→ 2 × $\sf \frac{22}{7}$ × 21

→ 2 × 22 × 3

→ 132cm.

∴ The circumstance of the circle with diameter 42cm is 132cm ${\boxed{\green{\checkmark{}}}}$

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(b) 9.1

Given diameter of the circle is :

• 9.1 cm

It's radius will be $\sf \frac{9.1}{2}$ = 4.55cm

Circumstance of the circle :

→ 2 × $\sf \frac{22}{7}$ × 4.55

→ 2 × 22 × 0.65

→ 28.6 cm

∴ The circumstance of the circle with diameter 9.1cm is 28.6cm ${\boxed{\green{\checkmark{}}}}$

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(c) 105cm

Given diameter of the circle is :

• 105 cm

It's radius will be $\sf \frac{9.1}{2}$ = 52.5cm

Circumstance of the circle :

→ 2 × $\sf \frac{22}{7}$ × 52.5

→ 2 × 22 × 7.5

→ 330 cm

∴ The circumstance of the circle with diameter 105cm is 330cm ${\boxed{\green{\checkmark{}}}}$

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Note behind :

• The radius of a circle is always the half of it's diameter.

Related formulae :

• Area of a circle = πr²
• Circumstance of a circle = 2πr.

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