A fair coin is flipped 60 times, what is the percent chance of flipping heads 25 or fewer times?
would you solve it this way?
P(X< or = 25)
so it's 60Cr * 0.5^(r) * 0.5^(60-r)
then that times 100 to get %.
It's a shortcut taken by comparing the Binomial distribution with the Normal distribution.
The calculation can then be done more quickly (especially when we'd have to sum a substantial number of terms of the Binomial expansion).
However, you'd need to have covered the Normal distribution for this.