I think the solution really depends on the complexity of the math problems you have in mind. Will they be very simple addition or subtraction problems, perhaps for children?
For simpler math problems, you can probably just create 2 random numbers and randomize an operator with something like the following:
x = int(random(1)) + 10
y = int(random(1)) + 10
operate = choose("+", "-", "/", "*")
MathString = str(x) & operate & str(y)
You can store a series of such strings within your array, then when you choose a random element out of the array, solve it using a special event sheet.
That'd be my own idea for a solution. Perhaps others may have better ideas.