52
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:   C) 75%



Explanation:

Let original radius = R.

New radius = 

Original area =  and new area = 

Decrease in area =  = 75%

Q:

The length, breadth and height of a room are in the ratio 7:3:1. If the breadth and height are doubled while the length is halved, then by what percent the total area of the 4 walls of the room will be increased  ?

A) 90% B) 88%
C) 85% D) 84%
 
Answer & Explanation Answer: A) 90%

Explanation:

Let length, breadth and height of the room be 7, 3, 1 unit respectively.

Area of walls = 2(l+b)xh = 2(7+3)x1 = 20 sq. unit.

Now, length, breadth and height of room will become 3.5, 6 and 2 respectively. 

Area of walls = 2(l+b)xh = 2(3.5+6)x2 = 38 sq. unit. 

% Increase in the area of walls = (38-20)x100/20 = 90%.

Report Error

View Answer Workspace Report Error Discuss

6 75
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 = 2r

=> 2 × 22/7 × r – r = 37

=> 37/7 × r = 37

=> r = 7 cm.

Diameter D = 2r = 7×2 = 14 cm.

Report Error

View Answer Workspace Report Error Discuss

9 108
Q:

The breadth of a rectangular field is 75% of its length. If perimeter of the field is 1050 m, what will be th area of field ?

A) 65700 sq.m B) 54500 sq.m
C) 78700 sq.m D) 67500 sq.m
 
Answer & Explanation Answer: D) 67500 sq.m

Explanation:

Let the length be 'l' and breadth be 'b'.

b = l × 3/4__________(a)

2(l+b) = 1050

l+b = 525___________(b)

From equations (a) and (b),

l = 300m, b = 225 m

Area = l × b

= 300 × 225

= 67500 sq.m.

Report Error

View Answer Workspace Report Error Discuss

7 178
Q:

The length of a rectangle is 10 cm more than the breadth. Find the diagonal length of rectangle if perimeter is 44 cm ?

A) 12.50 cm B) 14.21 cm
C) 15.98 cm D) 17.08 cm
 
Answer & Explanation Answer: D) 17.08 cm

Explanation:

Let the length of the rectangle = L cm

Then the breadth of the rectangle = (L - 10) cm

Perimeter of a rectangle = 2(L + B) cm

=> 44 = 2(L + L - 10)

=> 44 = 4L - 20

=> 4L = 64

=> L = 16 cm

=> B = L - 10 = 6 cm

Diagonal =  =   = 17.08 cm

Report Error

View Answer Workspace Report Error Discuss

8 168
Q:

In an old Palace there are 50 stairs to go on top floor. Each is 20 cm high, 30 cm wide and 60 cm long. If all the stairs are re-plastered at the rate of Rs. 4 per 100 sq.cm. What is the expenditure ?

A) Rs. 4680 B) Rs. 7600
C) Rs. 6000 D) Rs. 5480
 
Answer & Explanation Answer: C) Rs. 6000

Explanation:

Total are of all stairs = 50 (20x60 + 30x60)

= 50 (1200 + 1800)

= 50 x 3000

= 150000 sq cm.

Given rate of 100 sq cm = Rs. 4

Then for 150000 sq. cm = ?

=> 4 x 150000/100 = Rs. 6000

Report Error

View Answer Workspace Report Error Discuss

8 282