I teach excellent math students. In fact, most are rising juniors who will be taking AP Calculus. But that does not make them immune to making careless mistakes. I admit that their careless mistakes do add a touch of levity to our classes. However, careless mistakes are really not a laughing matter. They cost a serious loss of points. Here is a prime example of a careless mistake and the damage it did to my students’ math scores.

The May 2013 asked students to read the following chart and answer the following question:

ELECTRICITY USAGE FOR AN OFFICE BUILDING

MONTH USAGE IN MEGAWATT HOURS

May 10.76

June 12.53

July 17.60

August 16.49

September 14.24

The table above shows the monthly electricity usage for an office building from May to September. If the building’s usage in October was 3/5 of the combined usage for May and September, how many magawatt-hours were used in October?

OK, this Level 2 problem is very easy. All you have to do is add May (10.76) and September (14.24). The sum of these two months is 25 (very convenient). So 3/5 of 25 is 15. SIMPLE! Well imagine my surprise when 4 of my AP Calculus students missed this problem. They gave 14.32 14.32 as the answer. What? How did this happen? The answer is that they MISREAD the question. The four students carelessly substituted the word “TO” for the word “AND.” So they computed “the combined usage for May TO September” instead of “for May AND September.” This costly careless mistake lowered each student’s math score by 30 POINTS! You read this correctly. On the May 2013 SAT -1 equaled 770 for a loss of 30 points. Ouch!

I have decided to wage a holy war on careless mistakes. This will be the first in a new series of Blogs taking a close look at the causes of these pernicious errors.