If

111 + 168 = 2001
211 + 606 = 1201
521 + 926 = 1501
889 + 816 = 9091
169 + 898 = 6551
869 + 168 = 6851
251 + 696 = 1211
951 + 998 = 2201
651 + 268 = 1501
191 + 598 = 9201
291 + 998 = 8201

Then

105 + 509 + 588 = ?

• Do not think too far, this strange math have a very simple rule. Sep 26, 2016 at 9:00

105 + 509 + 588 = 1661

The equations all make sense if:

you look at them upside down! For instance, 111 + 168 punched into a calculator is actually 891 + 111 = 1002, which is 2001 upside down.

• you are a bit mistype, 861 must be 891. So what is the answer ? Sep 26, 2016 at 9:14
• Thanks for pointing that out, I was so caught up in getting it that I completely forgot to actually answer your question! Sep 26, 2016 at 9:19
• So $885+605+501=1991$ and the answer is $1661$. Why 5 and 2 are not respectively swapped turning upside down?
– z100
Sep 26, 2016 at 9:22
• @z100 If you punched 2 in calculator, it will still 2, not swapped wit 5. Sep 26, 2016 at 9:24
• my first green tick! fist pump thanks OP! Sep 26, 2016 at 9:34