Saturday, November 10, 2012

Quick Random Review Questions with Excel

One of my current uses of Microsoft Excel in the classroom is to quickly provide review questions for my students. I've used it in my Algebra classes to practice multiplications quickly by playing Around The World.
In order to set this file up, I used just one function - the randbetween() function. In B1 I entered the formula "=randbetween(1, 12)" which gives you an integer ("nice number") between 1 and 12.  I entered the same thing in D1 and now Excel gives me a random multiplication problem for the students to figure out.  The key is every time you press F9, it gives you another random problem.  This is because F9 "recalculates" each cell, which in this file effectively re-rolls the dice.

Of course it's customizable by altering the numbers in the function. Sometimes I'll challenge them and go up above 12. Or I'll throw negative numbers into the mix. Of if too many "easy" ones have been coming up, I'll make at least one of them range from 6 to 12 instead of 1 to 12. The possibilities are nearly endless.

A more advanced function, coupled with this idea, can make this tool all the more interesting.  Suppose you'd like to throw up different kinds of questions -- additions, subtractions, multiplications and/or divisions? If you'd like excel to choose one of them at random, you can use the choose function:
= choose( #,   "+",    "-",    "x",    "/")
This function will either give you a +, -, x, or / sign, depending on what # is.  If you type a specific number, say 3, then it will always give you the third choice, in this case "x".  If you instead type "randbetween(1,4)" in place of x, then it will randomly pick a number between 1 and 4, which will determine which operation to use. This effectively chooses a random operation of the four.  All together it would look like this:
= choose(randbetween(1,4),  "+",  "-",  "x",  "/")
The "" symbols around each of those operations are required, or excel will get confused and give you an error.

I typically don't display the answers, because I can calculate them as fast (or faster!) than the students and know if they are right or wrong, but if you wanted you could create a formula that calculates them for you.  If you have the same operation all the time, this is easy -- just type "=b1*d1" somewhere.  It is a little trickier if you have excel randomly choosing operations, and requires a slight tweak of the choose function above.
1. In a1, type "=randbetween(1,4)"
2. Change the choose function to read: "=choose(A1, "+", "-", "x", "/")
3. In a box where you want the answer displayed, type "=choose(A1, b1+d1, b1-d1, b1*b2, b1/b2)"

This is required because if you don't have a common cell (a1) to refer to when choosing the operation, you might have Excel choose to display a + sign, but display the answer to a subtraction problem, because a different random number was chosen in each cell. In this example, with four operations, it would be inconsistent 75% of the time, but by referring to A1, both the question and answer will always be the same.

By the way, if you want to stack the deck towards certain operations, you can have a choose function that looks like this:
= choose(randbetween(1,8) , "+", "+", "-", "-", "*", "*", "*", "*")
which would give you twice as many multiplication problems then adding or subtracting.

Also, I don't actually have them practice division problems like this because most of the time they would be decimals or fractions. If you want them to have divisible problems all the time, alter this template to show the answer to the multiplication problem.  Then show the answer and only one of the factors. Hide the other by making the column super thin, or making the font color white. This will guarantee that the divisions are always nice.

If you have this file available as a shortcut on your desktop, it is super quick to put up at the end of class if you have a few minutes available before the bell.