Probability Part 2

If n is number of trails, p is probability of success and q is probability of unsuccess then,
Mean =np and variance =npq.
Here
np+npq=24‌‌...(i)
np.npq=128‌‌... (ii)
and q=1−p‌‌...(iii)
from eq. (i), (ii) and (iii) : p=q=‌

1

2

and n=32.
∴ Required probability =p(X=1)+p(X=2)
=‌32C1⋅(‌

1

2

)32+‌32C2⋅(‌

1

2

)32
=(32+‌

32×31

2

)⋅‌

1

232

=‌

33

228