Since [tex]700=500+2\times100=\mu+2\sigma[/tex] is 2 standard deviations above the mean, you're looking for the probability that
[tex]\mathbb P(0<Z<2)[/tex]
The empirical rule says that approximately 95% of a normal distribution lies within 2 standard deviations of the mean, or [tex]\mathbb P(|Z|<2)\approx0.98[/tex].
Since the normal distribution is symmetric, you have
[tex]\mathbb P(|Z|<2)=2\mathbb P(0<Z<2)\implies \mathbb P(0<Z<2)\approx0.475\approx0.48[/tex]
