Probability distribution

An investment has an expected return of 10% with a standard deviation of 5%. If the returns are normally distributed, the probability of losing money is closest to?
Can someone help me solving this without referring the Z table

Generally, you couldn’t solve this without the Z table but there’s some special z you should memorize, such as 2.58 for 99% confidence interval; 1.96 for 95% and 1.64 for 90%.

In this case, z should be 2 which is closer to 1.96. Thus, the probability is closer to 2.5% (less than 2.5%).