Normal Distribution

#1
Hi,

I have a mean wealth of £102,000. I want to find the proportion of people below £17,500. i don't know the standard deviation, but I know the population size is 112,659. Is there any way of doing this? i saw a previous example where someone had used the standard deviation as: the mean divided by a spread coefficient of 2.5

Does this work as an estimate?

Thanks.