Sunday, 2 February 2014

T2B60

The answer is 4100.

If you're like me, you probably got 5000 the first time. Why? Because your brain adds 4 thousands, and by the time you reach the last ten, your brain is tricked into turning the "100" into "1000" because it seems nice. But if you do the math on a calculator (to check, not to cheat :P) or paper and pencil, you'll find:

 1000
+  40
--------
 1040
+1000
--------
 2040
+  30
--------
  2070
+1000
--------
  3070
+    20
--------
  3090
+1000
--------
  4090
+   10
--------
  4100

It's easier to see when it's vertical.

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