Simple math lesson on decimals (and percentages)

Yesterday my 5-year-old asked me what “point” meant.

At first I thought he meant “point something out”, but then I realized that my mom and I were talking about our solar production yesterday.I said I got less than 5.94kWh (which wasn’t horrible for a cloudy, rainy day) and my mom said “that’s nothing, one day I got .22”

And Tristan wanted to know what “point-twenty-two” meant.

First I tried talking about fractions which he’s been curious about lately, but that failed quickly.

Then pulled out my phone typed a number into my calculator and stated talking about tens places and hundreds places, but I guess they don’t cover that in kindergarten, so I did my best but it was clear he didn’t get it. Then inspiration struck.

I typed 0.60 on my calculator and said “if this was a battery, it would be 60% full.”

Then I did another: “if this was a battery, it would be 80% full.”

Then I tested him: “How full would this battery be?”


He got it! We did a few more then I typed in 5.94 and explained that this means if each battery was 1kWh I would have filled up 5 batteries. He said “and one more would be at 94%”.



I find it fascinating how knowledge shifts. When I was a kid I didn’t ever check battery levels. Percentages were more abstract but to Tristan they’re just a unit of measurement, like a clock.