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Q:

If the radius of a circle is decreased by 50%, find the percentage decrease in its area.

A) 55%	B) 65%
C) 75%	D) 85%

Answer & Explanation Answer: C) 75%

Explanation:

Let original radius = R.

New radius = $\frac{50}{100} R$ = $\frac{50}{100} R$

Original area = $\frac{R}{2}$ and new area = ${πR}^{2}$

$\frac{3 {πR}^{2}}{4} * \frac{1}{{πR}^{2}} * 100$

Decrease in area = $π {(\frac{R}{2})}^{2} = \frac{{πR}^{2}}{4}$ = 75%

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Filed Under: Area
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Q:

A college has 10 basketball players. A 5-member team and a captain will be selected out of these 10 players. How many different selections can be made?

A) 1260	B) 1400
C) 1250	D) 1600

Answer & Explanation Answer: A) 1260

Explanation:

A team of 6 members has to be selected from the 10 players. This can be done in $10 C_{6}$ or 210 ways.

Now, the captain can be selected from these 6 players in 6 ways.
Therefore, total ways the selection can be made is 210×6= 1260

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Q:

A sector of 120, cut out from a circle, has an area of $\frac{66}{7} c m^{2}$ . Find the radius of the circle ?

A) 1	B) 2
C) 3	D) 4

Answer & Explanation Answer: C) 3

Explanation:

Let the radius of the circle be r cm. Then,

$\frac{120}{360} {πr}^{2} = \frac{66}{7}$

$r^{2} = \frac{66}{7} * \frac{7}{22} * 3$

r=3.

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Q:

The inner circumference of a circular race track, 14 m wide, is 440 m. Find radius of the outer circle

A) 44	B) 22
C) 33	D) 84

Answer & Explanation Answer: D) 84

Explanation:

Let inner radius be r metres. Then, 2 $π$ r = 440 ; r = $440 \times \frac{7}{44}$ = 70 m.

Radius of outer circle = (70 + 14) m = 84 m.

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Q:

A wheel makes 1000 revolutions in covering a distance of 88 km. Find the radius of the wheel.

A) 14	B) 13
C) 12	D) 11

Answer & Explanation Answer: A) 14

Explanation:

Distance covered in one revolution = $\frac{88 \times 1000}{1000}$ = 88m.

$2 {πR}^{2} = 88 \Rightarrow 2 \times \frac{22}{7} \times R = 88 \Rightarrow R = 88 \times \frac{7}{44}$

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Q:

The diameter of the driving wheel of a bus is 140 cm. How many revolution, per minute must the wheel make in order to keep a speed of 66 kmph ?

A) 150	B) 250
C) 350	D) 550

Answer & Explanation Answer: B) 250

Explanation:

Circumference = No.of revolutions * Distance covered

Distance to be covered in 1 min. = (66 X1000)/60 m = 1100 m.
Circumference of the wheel = 2 x (22/7) x 0.70 m = 4.4 m.
Number of revolutions per min. =(1100/4.4) = 250.

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Filed Under: Area
Exam Prep: Bank Exams
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Q:

The area of a circular field is 13.86 hectares. Find the cost of fencing it at the rate of Rs. 4.40 per metre.

A) 2808	B) 3808
C) 4808	D) 5808

Answer & Explanation Answer: D) 5808

Explanation:

Area = (13.86 x 10000) sq.m = 138600 sq.m

${πR}^{2} = 138600 \Rightarrow R^{2} = 138600 \times \frac{7}{22} \Rightarrow R = 210 m$

Circumference = $2 {πR}^{2} = 2 \times \frac{22}{7} \times 210 = 1320 m$

Cost of fencing = Rs. (1320 x 4.40) = Rs. 5808.

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Filed Under: Area
Exam Prep: Bank Exams
Job Role: Bank PO

Q:

A room is half as long again as it is broad. The cost of carpeting the at Rs. 5 per sq.m is Rs. 270 and the cost of papering the four walls at Rs. 10 per sq.m is Rs. 1720. If a door and 2 windows occupy 8 sq. m, find the dimensions of the room.

A) b=6; l=18; H=6	B) b=5; l=6; H=18
C) l=6; b=18; H=15	D) l=5; b=18; H=18

Answer & Explanation Answer: A) b=6; l=18; H=6

Explanation:

Let breadth = x metres, length = 3x metres, height = H metres.

Area of the floor=(Total cost of carpeting)/(Rate) = (270/5) sq.m = 54 sq.m

$x \times \frac{3 x}{2} = 54 \Rightarrow x^{2} = 54 \times 2 \Rightarrow x = 6$

So, breadth = 6 m and length = $\frac{3 (6)}{2}$ = 9 m.

Now, papered area = (1720/10) = 172 sq.m

Area of 1 door and 2 windows = 8 sq.m

Total area of 4 walls = (172 + 8) sq.m = 180 sq.m

$2 \times (9 + 6) H = 180 \Rightarrow H = 6$

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