It has been found that 50.8% of U.S. households own stocks and mutual

funds. A random sample of 300 heads of households indicated that 173 owned some type of stock. At what level of significance would you conclude that this was a significant difference?
Compute the Test Value:

.577 -.508
Sq rt of (.508)(.492)/300

I am not understanding the lower part of this equation. I multiply the .508 x .492 then divide by 300. Then take the sq root of that and then divide by .069 (.577-.508).  And I am lost – I know I am not getting the right answer.

Help????
Please show me all the steps. ( only way I learn) 🙂

Thanks.

John