To be more specific and precise:
Here is the tab I have mentioned:
http://prntscr.com/36c82pSay player X has 10k of all kinds of army units and wants to launch 2 simultaneous attacks, X will click on
1/2 button to select
half of his army easily. If 3 simultaneous attacks are in case, then
1/3 button and same case with
1/4 button.