n <- 2:100

prob <- (pnorm(sqrt(n)/5) - pnorm(-sqrt(n)/5)) * (pchisq(1.44*n,n-1) - pchisq(0.64*n,n-1))

plot(n,prob)

abline(0.5,0)

cat("Sample size needed is: ",n[sum(prob<0.5)]+1,"\n");