Easiest way to play 16th note strums, usually rhythms that contain 16th notes ( also called sixteenth beats ) are not fast so what you do is actually divide the bars in 2; what does this mean; instead of counting every bar up to 4 the way explained before you count every bar to 8 or 2 times to four by just counting 1 and 2 and etc, this way every sixteenth note becomes an easy 8th note which is way more easy to strum and figure out. Also if the rhythm patterns get more difficult ( like 16th dotted 8th notes, 8th dotted 16th, 16th 8th 16th etc ) it will be almost imposibble with counting 1 e and a but divided becomes a piece of cake.

Hope this helps.

Herman