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- 21. The inner circumference of a circular race track, 25 m wide, is 880 m. Find radius of the outer circle.

A.152m

B.156m

C.163m

D.165m

Answer & Explanation

Answer: Option D

Explanation:**Let inner radius be r metres. Then, 2Πr = 880 ⇔ r = (880 x (7/44))= 140 m.**

Radius of outer circle = (140 + 25) m = 165 m.

Radius of outer circle = (140 + 25) m = 165 m.

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

A.52.5

B.60

C.72.5

D.75

Answer & Explanation

Answer: Option D

Explanation:**Let original radius = R. New radius =(50/100) R = (R/2)**

Original area=Π( R )

Decrease in area =((3Π(R )

Original area=Π( R )

^{2}= and new area= Π((R/2)^{2}= (Π( R )^{2})/4Decrease in area =((3Π(R )

^{2})/4 X (1/Π( R)^{2}) X 100) % = 75%- 23. In two triangle, the ratio of the areas is 4:3 and that of their heights is 3:4 the ratio of their bases is

A.16:9

B.9:16

C.9:12

D.16:12

Answer & Explanation

Answer: Option A

Explanation:**Given a1/a2 =4/3, h1/h2=3/4**

also, we know that

a1/a2=(1/2×b1×h1)/(1/2×b2×h2)

on substituting in above equation, we get

b1/b2= 16/9

therefore b1:b2= 16:9

also, we know that

a1/a2=(1/2×b1×h1)/(1/2×b2×h2)

on substituting in above equation, we get

b1/b2= 16/9

therefore b1:b2= 16:9

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