A boy walks to his school at a distance of 6km with constant speed of 2.5kmph and walks back with a constant speed of 4kmph. His average speed for round trip expressed in kmph is 

A)24/13 

B)40/13 

C)3 

D)1/2

If 10% of a radioactive material decays in 5 days, then the amount of original material left after 20 days is approximately:        
A) 70%     
B)75%                           
 C)65%                           
D)60%

The propulsion of a rocket is based on the principle of conservation of 

A)linear momentum

 B)energy 

C)angular momentum 

D)mass 

The propulsion of a rocket is based on the principle of conservation of
A) linear momentum
B)energy
C)angular
D)momentum mass

The curve represented by x = (cos t + sin t) and y = 5(cos t - sin t) is 
A)a circle 
B)a parabola 
C)an ellipse
D)a hyperabola
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If the charge flowing through a metal rod is halved and the temperature difference across
the ends of that rod is increased by 200 % the thomson heat absorbed or liberated

A) increases by 50 %
B) decreases by 50 %
c)increases by 100%
D)decreases by 25%

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1.6+2.9+3.12+.......+ n(3n+3)=

A)n(n+1) (n+2)
B)(n+1) (n+2) (n+3)
C)(n+2) (n+3) (n+4)
D)(n-1) n(n+1)
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