.15 or 3/20 on a ruler

I placed 5 tuna cans at various parts of my yard, and ran the sprinklers for 15 minutes. The total water in the 5 cans 3/4 of an inch. I'm trying to see what the average was for each can.

I took .75/5= .15 or 3/20 when u convert to fraction and reduce. How do I find that on a ruler?

I need to find out how long would I need to water in order to avg. an inch in each can.

So you poured four cans into the fifth, and got your 3/4 inch measurement that way?

That's a nice bit of work, and a very accurate procedure to accomplish what you're trying to do. My complements.

You don't need to convert your .15 inches to a traditional ruler measurement at all. You might express the rate of water application as "inches per minute", which is the same as inches divided by minutes. What you're looking for is "minutes per inch" of water, or minutes divided by inches.

And you've got some numbers to use: 15 minutes, and 0.15 inches. Divide 15 by 0.15, and you get a nice round number: 100 minutes per inch.

So run your sprinkler for 100 minutes (1 hour 40 minutes) and you will have laid down a inch of water.

3/20 which is equal to 2.4 sixteenths. I will round that up to 2.5 sixteenths. Each line on a ruler is a 16th. Count 2 and a half little lines and there you go.