Folks,
Continuing our post on thinking metric:
I am 5 feet 10 inches tall, or 70 inches. There are 2.54 centimeters per inch, so 2 times 70 = 140, then 0.5 * 70 = 35, so 140 + 35 = 175 cm is close, but we can calculate at 0.04 * 70 = 2.8 totals to 175 + 2.8 = 177.8 cm a more exact value.
Let’s try, 5 feet 4 inches = 64 inches: 64 * 2 = 128, now add 0.5* 64 = 32, plus .04 * 64 = 2.56 => 128 + 32 + 2.56 = 162.56 cm. The last step 0.04 * 64 is too tough, estimate by using 0.05 * 64 = 3.2. Some of these can be a little challening mentally, but get easier with practice.
Going the other way, multiply the height in cm by 0.4 to get inches. Say someone is 175 cm tall; how tall are they in inches? Multiply 0.4 * 175 = 70 inches or my height. It’s a little off, but close.
For weight, 1 kg = 2.2 pounds. So, if someone weighs 75 kg, that is 75 * 2.2 = 2 * 75 + 0.2 * 75 = 150 + 15 = 165 lbs. Going the other way, divide by two and then subtract 10%. Let’s try 165 lbs. Divide by 2 equals 82.5, subtract 10% then equals 82.5 – 8.25 = 74.25 kg, not too bad.
See the figure below for exact conversions,
Figure 1. Find exact conversions in this table.
Hopefully, after performing these mental calculations for a while, the metric values will become second nature.
Cheers,
Dr. Ron