776. Three sides of a triangular field are of length 15 m, 20 m and 25 m long respectively. Find the cost of sowing seeds in the field at the rate of 5 rupees per sq.m.
     

1. 1. $ 300
      

   
   
   

   2. $ 600
      

   
   
   

   3. $ 750
      

   
   
   

   4. $ 150

   
   
   

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1. View Hint View Answer Discuss in Forum

   15² + 20²= 25²
   ∴ The triangular field is right angled.
   

   =	1	× 15 × 20
   	2

   
   = 150 sq. metre
   Hence, Cost of sowing seeds = 150 × 5 = $ 750

   Correct Option: C

   15² + 20²= 25²
   ∴ The triangular field is right angled.
   

   =	1	× 15 × 20
   	2

   
   = 150 sq. metre
   Hence, Cost of sowing seeds = 150 × 5 = $ 750

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777. The radius of a circular wheel is 1.75 m. The number of revolutions it will make in travelling 11 km is : (use π = 22/7)
     

1. 1. 800
      

   
   
   

   2. 900
      

   
   
   

   3. 1000
      

   
   
   

   4. 1200

   
   
   

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1. View Hint View Answer Discuss in Forum

   Using Rule 7,
   The distance travelled by wheel in one revolution
   

   = 2πr = 2 ×	22	× 1.75 m = 11 m
   	7

   
   Therefore, the number of revolution to cover 11 km i.e. 11000 m by wheel
   

   =	11000	= 1000
   	11

   Correct Option: C

   Using Rule 7,
   The distance travelled by wheel in one revolution
   

   = 2πr = 2 ×	22	× 1.75 m = 11 m
   	7

   
   Therefore, the number of revolution to cover 11 km i.e. 11000 m by wheel
   

   =	11000	= 1000
   	11

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778. The radius of a wheel is 21 cm. How many revolutions will it make in travelling 924 metres ? (use π = 22/7)
     

1. 1. 7
      

   
   
   

   2. 11
      

   
   
   

   3. 200
      

   
   
   

   4. 700

   
   
   

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1. View Hint View Answer Discuss in Forum

   Using Rule 7,
   Circumference of wheel = 2πr
   

   = 2 ×	22	× 21 cm. = 132 cm
   	7

   
   

   ∴ Number of revolutions =	92400	= 700
   	132

   Correct Option: D

   Using Rule 7,
   Circumference of wheel = 2πr
   

   = 2 ×	22	× 21 cm. = 132 cm
   	7

   
   

   ∴ Number of revolutions =	92400	= 700
   	132

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779. A playground is in the shape of a rectangle. A sum of $ 1,000 was spent to make the ground usable at the rate of 25 paise per sq. m. The breadth of the ground is 50 m. If the length of the ground is increased by 20 m, what will be the expenditure (in rupees) at the same rate per sq. m. ?
     

1. 1. 1,250
      

   
   
   

   2. 1,000
      

   
   
   

   3. 1,500
      

   
   
   

   4. 2,250

   
   
   

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1. View Hint View Answer Discuss in Forum

   Using Rule 9,
   

   =	1000			= 4000 sq. metre
   		1
   		4

   
   

   ∴ Length =	4000	= 80 metre
   	50

   
   New length of field = 100 metre
   New area = 100 × 50 = 5000 sq. metre
   

   ∴ Required expenditure = $		5000 ×	1		= $1250
   			4

   Correct Option: A

   Using Rule 9,
   

   =	1000			= 4000 sq. metre
   		1
   		4

   
   

   ∴ Length =	4000	= 80 metre
   	50

   
   New length of field = 100 metre
   New area = 100 × 50 = 5000 sq. metre
   

   ∴ Required expenditure = $		5000 ×	1		= $1250
   			4

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780. If each edge of a square be doubled, then the increase percentage in its area is
     

1. 1. 200%
      

   
   
   

   2. 250%
      

   
   
   

   3. 280%
      

   
   
   

   4. 300%

   
   
   

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1. View Hint View Answer Discuss in Forum

   Using Rule 10,
   

   Percentage increase in area =		x + y +	xy		%
   			100

   
   Here, x = 100%
   y = 100%
   

   =		100 + 100 +	100 × 100		%
   			100

   
   = 300%

   Correct Option: D

   Using Rule 10,
   

   Percentage increase in area =		x + y +	xy		%
   			100

   
   Here, x = 100%
   y = 100%
   

   =		100 + 100 +	100 × 100		%
   			100

   
   = 300%

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