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Mathematics: Post your doubts here!

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The direction shuld be against the movement of the ring, but it is not.
see..since the system is in equilibrium...means upward = downward na?
but since the weight is 6
the upward force shld be 6 too
so logically it shld be same on both side (same magnitude on both side to obtain system in equilibrium)
but since 5cos30 is less than 6....logically friction is upward :)
u can check it with ths logic if u want :)
got it?
 
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Hello people, can you please help me in statistics may/june 2007 P6 Question 3b; the normal distribution one?? PLEASE I've been trying to get this done for months!
I am in hurry, cant edit post with symbols, hope you understand. :¬

Let the random variable X be normally distributed where with u(meu) n s(sigma) as mean n standard deviation respectively....
Nw we need to find
P((u+s)<X<(u-s))

Now standarising
we have
p{((u-s-u)/s)<Z<((u-s-u)/s)}
so, P(-1<Z<1)
so phi(1)-phi(-1)
=phi 1 -[1-phi(-1)]
={2phi(1)}-1
=(2*0.8413)-1
= .6826

therefore for 1 observation the p is .6862
so, for 800 it is .6826*800
=546 (Ans)
 
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