Started on percentages. I “taught” for about 2/3 of the class, solving several variations on 3.10.17 :

The January 2010 National Health Expenditures report stated that overall health care spending in the United
States rose from $7,421 per person in 2007 to $7,681 per person in 2008.

Computed absolute change as the difference, and relative change directly as a quotient, without going through absolute change:

$7.768/person

——————–  = 1.035

$7,421/person

That last number is unitless, and corresponds to a relative increase of 0.035 (subtracting the 1), which is 3.5% – literally, because “%” = “per cent” = “divide by 100″.

Then worked the problem given the old value and the percent increase, and, finally, given the new value and the percent increase. There the 1+ trick really helps you avoid saying “to find out what something was before a 50% increase, subtract 50% of it”. We saw that was wrong with a simple example!

Then started on homework problems. “three ten thousandths of one percent” gave them a lot of trouble. …

 

 

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