[CTcard]

I'd say a better lesson for a ten-year-old is that sarcastically calling out obvious (and trivial) typos is a petty kind of point-scoring that fosters neither good will nor stronger community.

How about this then: 
I apologize for mentioning the math mistake. 

I had thought it was kind of funny. Obviously you did not so I should be more careful.

[CTcard]

I'd say a better lesson for a ten-year-old is that sarcastically calling out obvious (and trivial) typos is a petty kind of point-scoring that fosters neither good will nor stronger community.

How about this then: 
I apologize for mentioning the math mistake. 

I had thought it was kind of funny. Obviously you did not so I should be more careful.