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Perimeter and Area Test - 27

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Perimeter and Area Test - 27
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  • Question 1
    1 / -0
    The perimeter of the following shaded portion of the figure is

    Solution
    Then length and breadth of rectangle is 17 m  and 4 m respectively.
    Then perimeter  of rectangle=$$2( L+B)=2(17+4)=42$$
    The radius of one fourth circle given in figure is 1 m
    Then perimeter of one fourth circle=$$\dfrac{1}{4}\times (2\pi r)=\dfrac{1}{4}\left ( 2\pi (1) \right )=\dfrac{1}{2}\pi $$
    Then perimeter of four one fourth circle=$$4\times \dfrac{1}{2}\pi =2\times 3.14=6.28 m$$
    Then perimeter of shaded figure $$= 42-6.28=35.72 m$$
  • Question 2
    1 / -0
    If the radius of a circle is 35 m, then the circumference of a circle is:
    Solution
    Given that, the radius of a circle is, $$r = 35\ m$$
    To find out: The circumference of the circle.

    We know that, the circumference of a circle is $$\displaystyle 2 \pi r$$

    $$\therefore \ $$ Circumference of the given circle $$=2 \times \dfrac{22}{7} \times 35\quad \quad \left[\because \ \pi=\dfrac{22}{7}\right]$$
    $$\therefore \ $$ Circumference $$= 220\ m$$

    Hence, if the radius of a circle is $$35\ m$$, the circumference of the circle is $$220\ m$$.
  • Question 3
    1 / -0
    Find the area of the parallelogram whose base is 16 cm and height 0.4 m ?
    Solution
    Base = 16 cm
    Height = 0.4 m
                = 0.4 $$\times$$ 100 = 40 cm
    Area of parallelogram = b $$\times$$ h
                                          = 16 $$\times$$ 40
                                          = 640 $$cm^2$$
  • Question 4
    1 / -0
    What will be area of a parallelogram with base 6 cm and altitude 3.5 cm?
    Solution
    Area of parallelogram = Base $$\times$$ Altitude
                                          = 6 cm $$\times$$ 3.5 cm
                                          = 21 square cm
  • Question 5
    1 / -0
    Find the area of a circle whose radius is 7 cm (in cm)
    Solution
    Area of a circle $$ = \pi {r}^{2} $$, where r is the radius of the circle
    Since $$r = 7$$
    So, area of the given circle $$ =  \pi \times 7 \times 7 = 49 \pi $$
  • Question 6
    1 / -0
    A well of diameter $$150\text{ cm}$$ has a $$30\text{ cm}$$ wide parapet running around it. Find the area of the parapet.
    Solution
    Diameter of well $$= 150\text{ cm}$$
    Radius of well = $$\displaystyle \frac{150}{2} = 75 \text{ cm}$$
    Width of parapet $$= 30 \text{ cm}$$
    Now, parapet of the well forms two circles.
    One is the inner circle and the second is the outer circle.
    Radius of inner circle $$(r) = 75 \text{ cm}$$
    Radius of outer circle $$R =$$ inner radius $$+$$ width of parapet $$= 75 + 30 = 105 \text{ cm}$$
    Area of parapet $$=$$ Area of outer circle $$-$$ Area of inner circle
    $$=\pi R^2 - \pi r^2 = \pi (R^2 - r^2)$$
    $$=\displaystyle \frac{22}{7} [(105)^2 - (75)^2]$$               
    $$=\displaystyle \frac{22}{7} \times 5400 $$
    $$=\displaystyle \frac{118800}{7} $$
    $$ = 16971.428 \text{ cm}^2$$
  • Question 7
    1 / -0
    If a square of area $$3$$ square units is inscribed in a circle, then the area of the circle is 
    Solution
    Given, area of a square $$=3$$ sq.cm
    Let $$a$$ be side of square.
    $$\Rightarrow$$  $$a^2=3$$
    $$\Rightarrow$$  $$a=\sqrt{3}$$ cm

    Diagonal $$=a\sqrt{2}$$
                    $$=\sqrt{3}\times \sqrt{2}$$ cm
                    $$=\sqrt{6}$$ cm

    Diameter of circle $$=$$ diagonal of square  $$=\sqrt{6}$$ cm

    Radius $$=\dfrac{\sqrt{6}}{2}\ cm$$
    $$\Rightarrow r=\dfrac{\sqrt{3}}{\sqrt2}\ cm$$

    $$\therefore$$  Area of the circle $$=\pi r^2$$
                                      $$=\pi\times \left(\dfrac{\sqrt{3}}{\sqrt2}\right)^2\ cm^2$$
                                      $$=\dfrac{3}{2}\pi\ cm^2$$

    Hence, the area of the circle is  $$\dfrac{3}{2}\pi\ cm^2$$

  • Question 8
    1 / -0
    If a circle is inscribed in a square of area $$4$$ sq units, then the area of the circle is 
    Solution

    $$\Rightarrow$$  Area of a square $$=4$$ square units.
    Let $$a$$ be side of square.
    $$\Rightarrow$$  $$a^2=4$$
    $$\Rightarrow$$  $$a=2$$ units.
    Diameter of circle and side of square are equal.
    $$\therefore$$  $$r=\dfrac{2}{2}=1$$ unit.
    $$\Rightarrow$$  Area of a circle inscribed in a square $$=\pi r^2$$
                                                                         $$=\pi\times (1)^2$$
                                                                         $$=\pi$$

  • Question 9
    1 / -0
    The diameter of a wheel is $$98\ cm$$ The number of revolutions it will have to make to cover a distance of $$1540\ m$$ is
    Solution
    Given the diameter of wheel is $$98\ cm$$
    Then radius of wheel =$$\dfrac{98}{2}=49\ cm$$
    Then circumference of wheel $$=2\pi r$$
    $$=2\times \dfrac{22}{7}\times 49=308\ cm$$
    the number of revolutions to be made to cover a  distance of $$1540\ m=\dfrac{1540\times 100\ cm}{308\ cm}$$
                                                                                                                         $$=\dfrac{154000}{308}=500$$
  • Question 10
    1 / -0
    If P represents the area and W represents the circumference of the circle, then P in terms of W is
    Solution
    Since P is the area so P = $$\displaystyle \pi r^{2}$$ ....(1)
    W is the perimeter thus W = $$\displaystyle 2\pi r\Rightarrow r=\frac{W}{2\pi }$$
    Put the value of $$r$$ in (1)
    $$\displaystyle \Rightarrow P=\pi \left (\frac{W}{2\pi }  \right )^{2}$$
    $$\displaystyle  P=\pi \frac{W^{2}}{4\pi ^{2}}$$
    $$\displaystyle  \Rightarrow P= \frac{W^{2}}{4\pi }$$
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