Using Excel Normal Dist for reliability calc?

If given MTBF and standard deviation can the reliabilty be predicted at a defined operational range using Excels Normaldistribution?
say mtbf = 50, sd= 20, then plug in the operating duration. NORMDIST(operating duration, 50, 20, true). Is that a way to calculate reliability at a specifed duration? thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.