FACTS  AND  FORMULAE  FOR  AREA  QUESTIONS

 

 

FUNDAMENTAL CONCEPTS :

I. Results on Triangles:

1. Sum of the angles of  a triangle is 180o

2. The sum of any two sides of a triangle is greater than the third side.

3. Pythagoras Theorem : In a right - angled triangle,

Hypotenuse2=Base2+Height2

4. The line joining the mid-point of a side of a triangle to the opposite vertex is called the median.

5. The point where the three medians of a triangle meet, is called Centroid. The centroid divides each of the medians in the ratio 2 : 1.

6. In an Isosceles triangle, the altitude from the vertex bisects the base.

7. The median of a triangle divides it into two triangles of the same area.

8. The area of the triangle formed by joining the mid-points of the sides of a given triangle is one-fourth of the area of the given triangle.

 

II.Results on Quadrilaterals :


1. The diagonals of a parallelogram bisect each other

2. Each diagonal of a parallelogram divides it into two triangles of the same area.

3. The diagonals of a rectangle are equal and bisect each other.

4. The diagonals of a square are equal and bisect each other at right angles

5. The diagonals of a rhombus are unequal and bisect each other at right angles

6. A parallelogram and a rectangle on the same base and between the same parallels are equal in area.

7. Of all the parallelogram of given sides, the parallelogram which is a rectangle has the greatest area.

 

IMPORTANT FORMULAE

I. 

1. Area of a rectangle = (length x Breadth)

Length =AreaBreadth  and  Breadth=AreaLength

2. Perimeter of a rectangle = 2( length + Breadth)

 

 

II. Area of square = side2=12diagonal2 

 

III. Area of 4 walls of a room = 2(Length + Breadth) x Height

 

 

IV.

1. Area of a triangle =12×base×height

2. Area of a triangle = s(s-a)(s-b)(s-c), where a, b, c are the sides of the triangle and s=12a+b+c

3. Area of an equilateral triangle =34×side2

4. Radius of incircle of an equilateral triangle of side a=a23

5. Radius of circumcircle of an equilateral triangle of side a=a3

6. Radius of incircle of a triangle of area  and semi-perimeter s=s

 

 

V.

1. Area of a parallelogram = (Base x Height)

2. Area of a rhombus = 12×Product of diagonals

3. Area of a trapezium = 12×(sum of parallel sides)×distance between them

    

 

VI.

1. Area of a cicle = πR2, where R is the radius.

2. Circumference of a circle = 2πR.

3. Length of an arc = 2πRθ360, where θ is the central angle.

4. Area of a sector = 12arc×R=πR2θ360 

 

VII.

1. Area of a semi-circle = πR22

2. Circumference of a semi - circle = πR

Q:

The length of a rectangle is 12 cm. What is the width if the area is 72 cm ?

A) 6cm B) 5cm
C) 3cm D) 4cm
 
Answer & Explanation Answer: A) 6cm

Explanation:

A=lb

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Q:

A wheelchair slalom event, athletes weave around cones and race to the finish line. A diagram of the rectangular course 30m length &16m bredth is shown. Find the the area of the course

A) 480 B) 560
C) 180 D) 460
 
Answer & Explanation Answer: A) 480

Explanation:

A = lw

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Q:

The difference between circumference and semidiameter of a circle is 37 cm. What is the diameter of the circle ?

A) 18 cm B) 12 cm
C) 16 cm D) 14 cm
 
Answer & Explanation Answer: D) 14 cm

Explanation:

circumference of a circle = 2πr

 

=> 2 × 22/7 × r – r = 37

 

=> 37/7 × r = 37

 

=> r = 7 cm.

 

Diameter D = 2r = 7×2 = 14 cm.

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Q:

Two concentric circles form a ring. The inner and outer circumferences of ring are  5187m and 3527 m respectively. Find the width of the ring.

A) 4 B) 5
C) 6 D) 7
 
Answer & Explanation Answer: A) 4

Explanation:

Let the inner and outer radii be r and R metres.

 

Then  2πR=3527=>R=3527*722*12=8m 

 

 2πR=5287=>R=5287*722*12=12m

 

=> Width of the ring = (R - r) = (12 - 8) m = 4 m.

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Q:

The length of a rope in meter by which a cow must be tethered in order that she may be able to graze an area of 2826 sq.m is ?

A) 15 mts B) 30 mts
C) 24 mts D) 36 mts
 
Answer & Explanation Answer: B) 30 mts

Explanation:

The cow can graze an area of 2826 sq.m i.e it is able to cover area of circle of 2826 sq.m

 

Therefore, πr2 =2826
r2 =(2826×7/22) = 899.18 = 900
r = 30 m.

 

Therefore, the radius of the circle implies the length of the rope = 30 mts.

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Q:

What is the length of the longest pole which can be kept in a room 12 m long, 4 m broad and 3 m high  ?

A) 13 m B) 14 m
C) 15 m D) 16 m
 
Answer & Explanation Answer: A) 13 m

Explanation:

The length of the longest pole which can be kept in a room 12 m long, 4 m broad and 3 m high is

 

=>  d2 = 122 + 42 + 32 = 13mts.

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Q:

A rectangular lawn of dimensions 80 m x 60 m has two roads each 10 m wide running in the middle of the lawn, one parallel to the length and the other parallel to the breadth. What is the cost of traveling the two roads at Rs.3 per sq m ?

A) Rs. 3600 B) Rs. 3800
C) Rs. 3900 D) Rs. 3700
 
Answer & Explanation Answer: C) Rs. 3900

Explanation:

Area = (l + b – d) d

= (80 + 60 – 10)10

=> 1300 sq.mts

=> 1300 x 3 = Rs.3900

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Q:

The sides of a right-angled triangle are 12 cm, 16 cm, 20 cm respectively. A new right angle Δ is made by joining the midpoints of all the sides. This process continues for infinite then calculate the sum of the areas of all the triangles so made.

A) 312 sq.cm B) 128 sq.cm
C) 412 sq.cm D) 246 sq.cm
 
Answer & Explanation Answer: B) 128 sq.cm

Explanation:

Area =   SSC Quiz : Quantitative Aptitude | 06 - 01 - 18 = 96

 

Sum of Area =  SSC Quiz : Quantitative Aptitude | 06 - 01 - 18

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