help on probabilty - binomial

[primer]

Dears,
I have an urgent request,
my daughter uses hpprime, student are studying probability at the moment, I'm really not an expert on that point myself, unfortunately.

She could find how to compute P(x=k) by using built-inbinomial(n,p,k)
But we could not find how to compute P(x<k) ?
anyone knows ?

I can't belive there is such option in hp prime.
cheap casio calc, offers function "Bcd" for that, what's the hp equivalent ?

Thank you.