Maths

I just got reminded of a very amusing incident that happened a few weeks back when I went to a school for another assignment.
That day, I was the I/C, ie I was the most senior guy there thus had to ensure that all the saikang was done properly. One of which was to count the number of people who attended the workshop for billing purposes and write it down on the receipt for the teacher in charge to sign. I finished doing that, then I used my handphone's calculator function to total the number of students up. I got the number 327, but I didn't write it down first, as I wanted to be very sure, as any mistake would mean having to rewrite everything on a fresh sheet. Having had to do that a few times, I was keen to avoid making the same mistake. Thus I passed the sheet to a new colleague of mine, asking her to help me check the total, before shifting my attention to something else for a while.
I settled the minor matter, and turned my attention back to the receipt. I was shocked to see my new colleague just staring at the sheet for a while, before passing it back to me with a confident "Yup, it's 327.". I was a bit flabbergasted, as I wholly expected her to use her phone's calculator as well to tabulate, but didn't want to waste time by questioning her, so I just took the paper back and redid the calculations using my phone's calculator. Satisfied that the number was indeed 327, I hurried to get the teacher to sign it and thus finish my duties.
When all that was done and dusted, we sat down and started to talk amongst ourselves. I heard my new colleague tell another colleague that she's doing Maths in NUS, and then it hit me. Again, it was one of those mouth move faster than brain moments, I dumbly blurted out "Oh that's why you didn't use a calculator!"
Good thing she found the good humor in my boo boo.
And during our monthly meeting last mon, we were supposed to guess what were each other's hobbies when we were 15. For her, I said confidently, "Abacus."