Problem solving with Chebyshev's inequality

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The symmetric coin is tossed 1600 times. What is the probability that the head will be shown up more than 1200 times?

I'm trying to solve this problem,but could not ot get correct answer. Can you help me?


Attempt. I should use Chebyshev inequality.

Using the formula $\mathbb{P}(|X-m|)>k)≤ var/k^2$

where m-mean, var - variance

Mean will equal = 800

Variance = 400

I put the numbers in it

$$\mathbb{P}(|X-800|>= 400)\le 400/400^2$$

But do not get the answer which is $\le 1/800$.