MAths 9709 p6 Doubt

[shressubha]

On any occasion when a particular gymnast performs a certain routine, the probability that she will
perform it correctly is 0.65, independently of all other occasions.
(i) Find the probability that she will perform the routine correctly on exactly 5 occasions out of 7.
[2]
(ii) On one day she performs the routine 50 times. Use a suitable approximation to estimate the
probability that she will perform the routine correctly on fewer than 29 occasions. [5]
(iii) On another day she performs the routine n times. Find the smallest value of n for which the
expected number of correct performances is at least 8. [2]

 

[shressubha]

A summary of 24 observations of x gave the following information:
Σ(x −a) = −73.2 and Σ(x −a)2 = 2115.
The mean of these values of x is 8.95.
(i) Find the value of the constant a. [2]
(ii) Find the standard deviation of these values of x. [2]

any 1 plzzz help me out