No complicated set-up for this one! Quite simply, what number comes next and why?
2 4 6 9 11 15 20 ??
The key to this puzzle is the problem title "Tango" which immediately brings the phrase "two to tango" to one's mind.
Now, writing the given numbers in Roman numerals, we get the sequence:
II, IV, VI, IX, XI, XV, XX
The next number, which can be written as Roman numerals having a string length of 2, is 40 whose Roman numeral equivalent is XL.
Consequently, the required number in the sequence following 20 must be 40.
Solution
