Counting tricks / counting by instinct

Something that I realized a few years ago is that there are some tricks to counting a small group of items much quicker than one at a time. For instance, how many X's are there on the next line?

XXXXXX

The only way to really know is to count them one by one, but if you let your instincts take over and just glance at them, your brain should be capable of coming up with the number 6 most of time. Apart from raw instinct, one trick is to use grouping, such as "how many sets of three does there look to be"? If there looks to be two sets of three, then you're dealing with 6. If there looks to be one more than two sets of three, you have seven, and if there looks to be one less than two sets of three, you have five.

Seven: XXXXXXX
Five: XXXXX

As for 1, 2, 3, and 4, you should be able to tell just by looking at the group of items.

For sets larger than 7, it gets more difficult, but with practice you can guess the size of sets less than 15 items about 40% of the time, and be at most one off 90% of the time.

Try these:

XXXXXXXX

XXXXXXXXXX

XXXXXXXXXXXXX

For the bigger ones you can't really rely on counting tricks, you just have to use your "jedi" instincts and make the best possible / most likely guess.