How we got 2009
Step 1: Multiply «
the first digit» by «
itself plus one». This forms the first part of our answer.
4 x (
4 +
1) =
20
Step 2: Multiply the last two digits to get the second part of our answer.
1 x
9 =
09
Note that we add an extra zero if the product is less than 10. Here the answer is 2009 and not 209.