z score Chebyshev’s theorem

Standardize the data 10, 21, 23, 27, 27, 29, 30, 32, 33, 40, then identify
the percentage of observations that fall within k = 2.0
standard deviation units from the mean. Do the results
support Chebyshev’s theorem?

I found
mean 27.2
s=8.052

then I found all Zi and sumed them where I have z=0 dhe xs=1

27.2-+2*8.052 (11.096 43.304)

I dont know why the result in book is 90%

because if we use for k=2 than (1-1/2^2) is 0.75

if we check for 2 standard deviation than we have 95%