Eleven members of the middle school math club each paid the same amount for a guest speaker to talk about problem solving at their math club meeting. they paid their guest speaker $1−a−2−. what is the missing digit a of this 3-digit number?

So what we know is that there is a number 1?2 that is divisible by 11.

what was 11 multiplied by to get this number?  it must start with "1" since 1*1=1 and end with "2" since 1*2=2 and there is 2 at the end of the product .

so let's try: what is 11*12? 132? yes, that sounds good!

so the missing number is 3 and they each paid 12 dollars.