TAX DAY:

There was a taxpayer rally at the Capitol today. From a vantage point in the glass bank building I could see the rally. I estimate perhaps 5000 plus participants. How do I get that number?

Look at the rally. Count out a block of 10 people. Then use that size to create a block of 100. Use that block to estimate the crowd. (How many blocks of 100 do you see.)

Try it for yourself, it's fun.