## Prime Number Problem and Gender Bias

This morning, my friend AJ called to ask for help in solving a problem from his ten-year-old daughter’s homework. When he explained his dilemma, the first thing I did, of course, was laugh. “Wow,” I said. “You really aren’t as smart as a fifth-grader, are you?”

AJ and his daughter are both intelligent, and his daughter loves math. The problem they were trying to solve was this:

What is the units digit of the product of the first 21 prime numbers?

You can use this list of prime numbers if you need some help. As a hint, the 21st prime number is 73 (which, incidentally, is the Chuck Norris of numbers).

Once you solve the problem, of course, you realize that the problem would have the same answer if asked as follows:

What is the units digit of the product of the first n prime numbers, for n > 3?

This made me think that this could be a good problem for the classroom. Have all students randomly generate a positive integer, and then have them solve the problem above using their random number to replace n. It would be impactful for students to see that everyone gets the same answer; and those who multiplied things out might be compelled to look for a pattern and figure out why everyone got the same answer.

But then I realized: this problem is gender biased. Well, maybe. The problem asks for the units digit of the product of the first 21 prime numbers. The choice of 21 was very deliberate, I’m sure. It’s small enough that an industrious student might actually try to calculate the product. In my experience, female students are more industrious than males and therefore more likely to do the computation. But the number is large enough that male students, who are lazy like I am, will think, “That’s too much work. There’s got to be a trick!”

I mentioned to AJ that if a larger number were chosen — for instance, if it involved the product of the first 1,000 prime numbers — then it might be more obvious that students ought to look for a pattern. “You haven’t met my daughter,” he said. “She’d still try to compute it.”

You may think my assertion is crazy. There is nothing in the problem that appears inherently biased against females.

A few years ago, the AAUW published a report about gender bias in math questions. One of the selected questions was something like, “What is the value of n if n + 2 = 7?” Despite the neutrality of the content, girls scored significantly lower than boys on this question, so it was deemed to be biased. (Sorry, I wasn’t able to find a reference to the report. If anyone knows the report to which I’m referring, please share in the comments.)

Further, FairTest claims that the gender gap all but disappears on all types of questions except multiple choice when other question types were examined on Advanced Placement tests. What is it about multiple choice questions that makes them implicitly unfair to females? I have no idea.

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• 1. zachdcox  |  April 29, 2012 at 9:16 pm

>= 3

• 2. venneblock  |  April 30, 2012 at 8:58 pm

Good catch!

• 3. JimsMaher  |  April 30, 2012 at 11:10 pm

Number bias is every gender’s problem.
If you’re your only focus is numbers, be forewarned …
I’ve sworn to scorn and adorn them with thorns.
Guess it.
Numbers don’t count.
Numbers alone are meaningless.
It’s the difference between that gets this,
an operator and an operand.
The gender’s only operate cause they can … in relationships.
… and numbers only calculate when it’s sanctioned with arithmetic.

Case in point, 666 is only fancy-dancy-prancy cause it’s Auntsy Nancy was DCLXVI, fat chancy clancy, it’s worth squat, zziippo zero zilch, in value to your mind if they worry’s already there.
Square.

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