$($c$)$ Use the Chebyshev inequality to determine how many times a

balanced coin must be tossed in order that the probability will be

at least $0\mathrm{.}80$ that the ratio of the observed number of heads to the

number of tosses will be between $0\mathrm{.}4$ and $0\mathrm{.}6$

$(7$ mks$)$