How to drop a specific percentage of ICMP"Echo Request"

Hello, I am trying to create a rule to drop ICMP, but just 10 percentage of the packets, is it possible ?
And one other question, I am trying to do a telnet from my router to a website in port 80, I can see the ( SYN) from my mikrotik to the site
and a (SYN, ACK ) from the site to the mikrotik, after I just see re transmissions, I need to create a rule to allow traffic from my router to the web ?
Thanks!