Chris Peterson wrote:
since "old timers" learned their 'rithmatic without calculators, most can do a bit of simple reckoning in their heads, no?
Kilometers times two divided by three will get you in the miles ballpark.
Dividing by three in one's head (or on paper) can be tricky at times.
Try: kilometers times six and then shift the decimal point.[/quote]
300,000 km/s => 1,800,000 => 180,000 m/s
For miles to kilometers: miles doubled 4 times and then shift the decimal point:
186,000 m/s => 372,000 => 744,000 => 1,488,000 => 2,976,000 => 297,600 km/s