Question

a coin of radius 28mm . what is the area in (a)mm2 (b)cm2 no spamming from internet and no use of answers will be reported and correct answers will mark as a braniliest please help​

Answer 1

$\bf\implies \boxed{\bf{Area \: of \: circle = \pi r{}^{2} }}$

a) In mm² ?

Ans.- Given radius = 28mm

$\sf \: Area \: of \: circular \: base \: of \: coin = \pi(r) {}^{2}$

$\sf \: \: \: \: \: \: \: \: = \dfrac{22}{7} \times 28mm \times 28mm$

$\sf \: \: \: \: \: \: \: \: = \dfrac{22}{7} \times 784mm {}^{2}$

$\sf \: \: \: \: \: \: \: \: = \boxed{ \purple{\sf{ 2464mm {}^{2} }}}$

ㅤ

b) In cm² ?

Ans.- We've to convert mm into cm.

Radius = 28mm = 28/10cm = 2.8cm

Again,

$\sf \: Area \: of \: circular \: base \: of \: coin = \pi(r) {}^{2}$

$\sf \: \: \: \: \: \: \: \: = \dfrac{22}{7} \times 2.8 \times 2.8$

$\sf \: \: \: \: \: \: \: \: = \dfrac{22}{7} \times 7.84cm {}^{2}$

$\sf \: \: \: \: \: \: \: \: = \dfrac{172.48}{7}$

$\sf \: \: \: \: \: \: \: \: = \boxed{ \purple{ \sf24.6cm {}^{2} }}$

___________________________

• Coin is in cylindrical shape

➸ Total surface area of cylinder = 2πr( r+h ).

➸ Curved surface area of cylinder = 2πrh

➸ Volume of cylinder = πr²h

➸ Perimeter of circle = 2πr

Answer 2

Given:-

• Radius of the coin = 28mm

To find:-

• Area of this coin in mm² and cm²

Formula to be used:-

$\underline{\boxed{\sf area\: of \: Circle = πr²}}$

Solution:-

Area of the coin in mm² :-

$\longrightarrow$ area = $\sf\dfrac{22}{7}$ × 28²

$\longrightarrow$ area = $\sf\dfrac{22}{7}$ × 28 × 28

$\longrightarrow$ area = 22 × 4 × 28

$\longrightarrow$ area = 2464mm²

Area of Coin in cm² :-

• Let's convert the radius of the coin which is given in mm info cm.

we know that 1 mm = $\sf\dfrac{1}{10}$ cm

$\longrightarrow$ Radius = 28 mm = $\sf\dfrac{28}{10}$cm = 2.8 cm

Now, Area of this coin :-

$\longrightarrow$ area = $\sf\dfrac{22}{7}$ × 2.8²

$\longrightarrow$ area = 24.6 cm²

_________________________

Additional information:-

• Total surface area of cylinder :-

$\longrightarrow$ $\underline{\boxed{\sf T.S.A = 2π2(r+h}}$

• Curved surface area of cylinder

$\longrightarrow$ $\underline{\boxed{\sf C.S.A = 2πrh}}$

• Volume of cylinder

$\longrightarrow$ $\underline{\boxed{\sf Volume = πr²h}}$