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Q:

The diagonal of a rectangle is $\sqrt{41}$ cm and its area is 20 sq. cm. The perimeter of the rectangle must be:

A) 18	B) 28
C) 38	D) 48

Answer & Explanation Answer: A) 18

Explanation:

$\sqrt{(l^{2} + b^{2})} = \sqrt{41}$ (or) $l^{2} + b^{2} = 41$

Also, $l b = 20$

${(l + b)}^{2} = l^{2 +} b^{2} + 2 l b$ = 41 + 40 = 81

(l + b) = 9.

Perimeter = 2(l + b) = 18 cm.

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Q:

The percentage increase in the area of a rectangle, if each of its sides is increased by 20%

A) 22%	B) 33%
C) 44%	D) 55%

Answer & Explanation Answer: C) 44%

Explanation:

Let original length = x metres and original breadth = y metres.

Original area = xy sq.m

Increased length = $\frac{120}{100}$ and Increased breadth = $\frac{120}{100}$

New area = $\frac{120}{100} x * \frac{120}{100} y = \frac{36}{25} x y m^{2}$

The difference between the Original area and New area is:

$\frac{36}{25} x y - x y$

$\frac{11}{25} x y$ Increase % = $(\frac{\frac{11}{25} x y}{x y}) * 100$ = 44%

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Q:

The ratio between the perimeter and the breadth of a rectangle is 5 : 1. If the area of the rectangle is 216 sq. cm, what is the length of the rectangle?

A) 16	B) 18
C) 20	D) 22

Answer & Explanation Answer: B) 18

Explanation:

$\frac{2 (l + b)}{b} = \frac{5}{1}$ => 2l + 2b = 5b => 3b = 2l

b=(2/3)l

Then, Area = 216 cm²

=> l x b = 216 => l x (2/3)l =216

l = 18 cm.

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Q:

If there are 15 dots on a circle,how many triangles can be formed?

A) 455	B) 450
C) 469	D) 500

Answer & Explanation Answer: A) 455

Explanation:

There are 15 dots in total,and to make a triangle we need to select any three of those dots.

So, $15 C_{3}$ = 455

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Filed Under: Permutations and Combinations

Q:

There are 7 non-collinear points. How many triangles can be drawn by joining these points?

A) 10	B) 30
C) 35	D) 60

Answer & Explanation Answer: C) 35

Explanation:

A triangle is formed by joining any three non-collinear points in pairs.

There are 7 non-collinear points

The number of triangles formed = $7 C_{3}$ = 35

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Filed Under: Permutations and Combinations

Q:

A right triangle with sides 3 cm, 4 cm and 5 cm is rotated the side of 3 cm to form a cone. The volume of the cone so formed is:

A) 12 pi cub.cm	B) 15 pi cub.cm
C) 16 pi cub.cm	D) 20 pi cub.cm

Answer & Explanation Answer: A) 12 pi cub.cm

Explanation:

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Filed Under: Volume and Surface Area

Q:

The length of a rectangle is halved, while its breadth is tripled. What is the percentage change in area?

A) 25% increase	B) 50% increase
C) 50% decrease	D) 75% decrease

Answer & Explanation Answer: B) 50% increase

Explanation:

Let original length = x and original breadth = y.

Original area = xy.

New length = x/2 and New breadth = 3y.

New area = (x/2 * 3y) = (3/2 )xy

Therefore, Increase % = [(1/2)xy * (1/xy) * 100] % = 50%

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Q:

The difference between the length and breadth of a rectangle is 23 m. If its perimeter is 206 m, then its area is:

A) 1520 sq.m	B) 2420 sq.m
C) 2480 sq.m	D) 2520 sq.m

Answer & Explanation Answer: D) 2520 sq.m

Explanation:

We have: (l - b) = 23 and 2(l + b) = 206 or (l + b) = 103.

Solving the two equations, we get: l = 63 and b = 40.

Area = (l x b) = (63 x 40) sq.m

= 2520 sq.m

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Filed Under: Volume and Surface Area

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