You need to assume a distribution, and I'm going to assume you mean a Normal distribution (but not everything has a Normal distribution just to point this out).

The normal distribution N(0,1) has the PDF of f(x) = [1/SQRT(2*pi)] * e^(-x^2/2) and probability of P(Z < a) = Integral of f(x)dx from -infinity to a.

So based on these hints, what can you say about the probability (i.e. percentage) given this information?