### Brain Teasers

# 5, 15, 27, ...

What are the next two numbers in this series?

5, 15, 27, 45, 63, 81, __, __

5, 15, 27, 45, 63, 81, __, __

### Hint

It has to do with the digit numbers.### Answer

The next two numbers are 99 and 135.The pattern is:

Take the digits like "5" for example, and multiply it by 2, you get 10. 5 plus 10 equals 15. For 15, one plus five (the digits!) equals 6. 6 multiplied by 2 is 12. 12 + 15 equals the next number, 27.

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## Comments

Very hard!

It's become a very simple teaser actually, due to the special nature of 9..

All multiples of 9 have their sums add up to 9. (9, 18, 27, 36, 45... so on)

Since we're always going to get the addition of 2 X 9, from this point on the sequence becomes a very simple:

Add 18. Add 18. Add 18. Add 18....

All the other work isn't necessary anymore.

All multiples of 9 have their sums add up to 9. (9, 18, 27, 36, 45... so on)

Since we're always going to get the addition of 2 X 9, from this point on the sequence becomes a very simple:

Add 18. Add 18. Add 18. Add 18....

All the other work isn't necessary anymore.

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