Maths Dr. T.K. Jain. AFTERSCHOOOL M: 9414430763
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The length of minute hand on a wall clock is 7cms. What is the area swept by the minute hand in 30 minutes?
• This is the question of circle • Area of circle : pi *r*r = 22/7*7*7=154 • But the area in 30 minutes will be half circle – so it will be 77 sq cm.
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A wheel makes 1000 revolution in covering a distance of 88 km. What is diameter of the wheel?
• The circumference of wheel = 88000 / 1000 = 88. • Formulae of circumference of circle = 2pi*r = 2*22/7*R = 88 • 2R = 88*7/22 = 28meters Ans.
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A wire is in the form of an equilateral triangle with area 5 sq. m. If its shape is changed to a circle, its radius will be? • Area of Triangle: 3^1/2/4 *side*side • 3^1/2/4 *side*side =5, • side^2 = 20/ 3^1/2 =11.5 Side = 3.4 approx. Length of wire:3*3.4= 10.2 Circumference of circle =10.2 2pi *r = 10.2 R = 10.2/ 6.28 = 1.63 meters approx.
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What is the circumference of semicircular shape on a line of length 10 cm? • • • •
Circumference = 2pi*r =2*22/7*5 =10*3.1428 = 31.42 Half of circumference = 15.92 Add diameter with this = 25.92 ans.
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The ratio of the length of a side of an equilateral triangle and its height is? • Let us assume that side of a triangle is X. its area is .433 X^2. (3^1/2/4 *side * side). Let us assume that we divide it in two triangles of equal size with area = .433 X^2/2. This triangle will have area ½*base*height. (being right angle triangle) • Here base = side /2, so • .433x^2 /2 =1/2*X/2*h • Height = .433x^2*4 /2x = .433 *2 X • Ratio of side to height = 1: .866 Ans. • Another method = applying pythogorus rule, • X^2 = (x/2)^2 + height ^2 , solving we get ratio of side to height as 2:3^1/2 www.afterschoool.tk
There are 4 circles in a bigger circle. The diameter of biggest circle is 56 but those of smaller circles is 7. what is area •of bigger circle which has not been occupied by smaller circles.
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Answer: • Area of bigger circle: • 3.1428*28*28 =2464 • Area of smaller circle = 22/7*7/2*7/2 = 38.5 ; there are four circles so area is 38.5*4 = 154 • Area of uncovered bigger circle • 2464-154 = 2310 ans. www.afterschoool.tk
Inner circumference of a 14 meter wide race track is 440 meters, what is the radius of outer circle?
• Inner radius is • 2pi*r = 440; r = 440*7/44 = 70 • Radius of outer circle is 70+14 = 84 ans.
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A circular wire of radius 42 cm is bent into the shape of a rectangle. What is the diagonal of this rectangle, if the sides are in the ratio of 6:5?
Step 1: find the circumference : 2*pi*r = 2*22/7*42 =264 6x+5x = 264; 11x=264; x =24 Length of rectangle : 144, width is 120. • Diagonal will be square root of 144^2 +120^2= 187.44 approx. • • • •
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What is the area of circle inscribed in an equilateral triangle of side 24? • • • • •
We know that radius of incircle is : R = Side /( 2*3^1/2) Therefore radius is : 24 / (2*1.73) =6.928 Area of circle = pie *r *r = 150.8 approx. ans.
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What is the area of circle circumscribed in an equilateral triangle of side 24?
• We know that radius of circumcircle is : • R = Side /3^1/2 • Therefore radius is : 24 / 1.73 • =14aprox • Area of circle = pie *r *r • = 196 pi. Ans. www.afterschoool.tk
A man builds a circular pool of radius 5 inside a circular garden of radius 12. In order to compensate for area lost, he extends the garden, What is radius of garden, if its area is same as earlier? • • • • • • • •
Area of garden: 144 pi. Area of pool=25 pi Let us assume that he increases radius by x Pi * (12+x)^2 -144pi = 25 pi. 144+24x+x^2-144 = 25 X^2+24x-25 =0 X^2 +25x-x-25; x(x+25)-1(x+25) X=1 New radius of the garden is 13 Ans.
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What is the area of largest triangle that can be inscribed in a semi-circle of radius 7?
• Here we will keep the base as diameter of the circle = 14. Height will be 7 (as radius). • Thus the area will be ½*7*14 • =49 ans.
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What is the area of largest triangle that can be inscribed in a circle of radius 7? • • • • •
Radius = side / 3^1/2 Side= Radius * 1.73 = 7*1.73 =12.12 Area of triangle: 3^1/2 /4 * 12.12*12.12 =63 approx. ans.
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What is the area of largest square that can be inscribed in a circle of radius 7? • Diagonal of square is 14. • Area of square is ½ *Diagonal * diagonal. • ½*14*14 = 98 ans.
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What is the area of largest hexagon that can be inscribed in a circle of radius 7? • Hexagon will have one side equal to radius = 7. • Hexagon is 6 multiplied to 3^1/2/4*side *side. • =21.21*6 • Area of hexagon = 127 approx.
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We don’t want a cow to graze more than 9856 sq m area in circular form. What should be the length of rope by which we should tether the cow?
• We have to calculate the radius in this question. • Pi*r *r = 9856 • R^2 =9856 / pi = 3136 • R = 56 ans.
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The ratio of radii of two circles is in the ratio of 1:2, what is the ratio of their area?
• 1:4 ans.
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The ratio of radii of two circles is in the ratio of 1:2, what is the ratio of their circumference? • 1:2 ans.
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The ratio of radii of two spheres in the ratio of 1:2, what is the ratio of their volume? • 1:8 ans.
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The ratio of sides of two cubes is in the ratio of 1:2, what is the ratio of their volume? • 1:8
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