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Perimeter and Area Test - 11

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Perimeter and Area Test - 11
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  • Question 1
    1 / -0
    Perimeter of a triangle is the sum of the lengths of all the ............ sides.
    Solution
    Perimeter of a triangle is the sum of the lengths of all the three sides.
  • Question 2
    1 / -0
    What is the area of the given figure? $$ABCD$$ is a rectangle and $$BDE$$ is an isosceles right triangle.

  • Question 3
    1 / -0
    If the radii of two concentric circles are $$15\ \text{cm}$$ and $$13\ \text{cm}$$, respectively, then the area of the circulating ring in sq. cm will be:
    Solution
    $$R = 15\ \text{cm}, r = 13\ \text{cm}. $$
    Area of the circulating ring $$= \pi (R^2-r^2)$$
    $$= \cfrac {22}{7} ({15}^2-{13}^2)\ \text{cm}^2$$
    $$= \cfrac {22}{7} \times 28 \times 2\ \text{cm}^2$$
    $$=176\ \text{cm}^2$$ 

  • Question 4
    1 / -0
    The diameter of each circle shown in the given figure is 'd'  then the area of the square is given by

    Solution
    There are 3 circles of diameter 'd
    So side of the square is 3d and 
    Hence area is   $$side^2=\displaystyle 9d^{2}$$
  • Question 5
    1 / -0
    The area of a circle is 301.84 $$\displaystyle cm^{2} $$ Then its radius is
    Solution
    Area of the circle = $$\displaystyle \pi r^{2}$$
    According to the question,
    $$\displaystyle \pi r^{2}=301.84$$
    $$\displaystyle \Rightarrow \frac{22}{7}r^{2}=301.84$$
    $$\displaystyle r^{2}=\frac{7\times 301.84}{22}=96.04$$
    $$\displaystyle \therefore r=\sqrt{96.04}=9.8\ cm$$
  • Question 6
    1 / -0
    A circular park has a path of uniform width around it. The difference between the outer and inner circumferences of the circular park is $$132$$ m. Its width is
    Solution
    Let $$r_1$$ and $$C_1$$ be the radius and the circumference of the inner circle.
    Let $$r_2$$ and $$C_2$$ be the radius and the circumference of the outer circle.
    The width of the circular path is $$(r_2-r_1)$$ m.
    Given, $$C_2-C_1=132$$ m
    $$\Rightarrow 2\pi r_2 - 2\pi r_1=132$$
    $$\Rightarrow 2\pi (r_2-r_1)=132$$
    $$\Rightarrow r_2-r_1=\cfrac{66}{\dfrac{22}{7}}$$
    $$\Rightarrow r_2-r_1=21$$
    Thus, width of the circular path is $$21$$ m.

  • Question 7
    1 / -0
    The radius of a circle whose area is equal to the sum of the areas of two circles of radii 5 cm and 12 cm is
    Solution
    We know that area of a circle of radius $$r = πr ^2 $$
    By given condition, 
    $${ A }_{ 3 }={ A }_{ 1 }+{ A }_{ 2 }$$ .....(1)
    Since, $$r_1 = 5$$ & $$r_2= 12$$ 
    So, by (1), we have
    $$ { \pi r }^{ 2 }={ \pi 5 }^{ 2 }+{ \pi 12 }^{ 2 }\\\\ { r }^{ 2 }={ 5 }^{ 2 }+{ 12 }^{ 2 }\\\\ r=\sqrt { 25+144 } =\sqrt { 169 } =13 \text{ cm}$$
  • Question 8
    1 / -0
    The radius of a circle is increased by 1 cm. Then the ratio of new circumference to the new diameter is
    Solution
    New radius = $$(r+1)\ \mathrm{cm} $$
    Ratio = $$2\pi (r+1):2(r+1)=\pi :1$$
  • Question 9
    1 / -0
    From a square metal sheet of side $$28\;cm$$, a circular sheet is cut off. Find the radius of the largest possible circular sheet that can be cut. Also find the area of the remaining sheet.
    Solution
    Area of square sheet $$=$$ $${ (28) }^{ 2 }=784{ cm }^{ 2 }$$

    The largest circle of diameter equals to the side of square can be cut off from the square sheet.

    $$\therefore $$ Radius of circular sheet $$=$$ $$\dfrac { 28 }{ 2 } =14cm$$

    Area of remaining sheet $$=$$ $$784-\pi { r }^{ 2 }=784-\dfrac { 22 }{ 7 } \times 14\times 14$$
                                             
                                             $$=$$ $$784 - 616$$ = $$168$$$${ cm }^{ 2 }$$
  • Question 10
    1 / -0
    If the perimeter and area of a circle are numerically equal then the radius of the circle is 
    Solution
    $$\textbf{Step 1: Substitute area of circle and perimeter of circle formula in the given condition}$$
                   $$\text{Area of circle}=\pi r^2$$
                   $$\text{Perimeter of circle}=2\pi r$$
                   $$\text{Given that area and perimeter are numerically equal}$$
                   $$\implies \pi r^2=2\pi r$$
                   $$\implies r=2$$

    $$\textbf{Thus, the required radius of the circle is 2 units}$$
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