How to ignore alphanumeric (non-numeric) input

I am wondering how to get columns E and F to ignore alphanumeric entries.
I already entered in the data to the attached spreadsheet so you can see. People will copy and paste data in here and I need it to ignore anything that is not a number.
How do I do this?

Thanks!

i am still trying to resolve this. no luck yet. I have tried conditional formatting, but sitll cant get it to ignore those rows with non-numeric.\

ideas?

Ill give it a try. Thanks.

ok, that worked. now onto the next issue. In position D12 I have it set to calculate the total number of entries. How can I tell this number to ignore any non alphanumeric entries into E and F columns?

p.s. you guys are awesome. I try to follow what you tell me and learn myself, but some of this is so far beyond me.

Thanks in advance again.

Any ideas?