[jiggyboy]

5. an arithmetical problem to be solved, or such a problem worked out and having the various steps shown.

http://www.dictionary.com/browse/sum?s=t

I had to look it up myself. This particular usage is probably used more in England than it is here.

[ProtectOurFreedom]

Funny, the Oxford dictionary didn’t have the definition of “sums” as a colloquialism for any math problem. I expected to see “Chiefly Brit.”