S.O.S. Mathematics CyberBoard

I took an online Algebra quiz, and one of the problems states:

You start a cycling club and want to have every member recruit 3 new members at the end of each month. You are the only member of the club at the end of April, 2013. If your plan is carried out, how many members will be in the club at the end of:

May, 2013?
June, 2013?
July, 2013?
January, 2014?

I took the number of members at the end of each month and multiplied by 3, giving the answers:

May, 2013, 4
June, 2013, 12
July, 2013, 36
January, 2014, 26,244

After submitting the quiz, it said that was incorrect, and that the number of members at the end of each month should be multiplied by 4, giving the totals of:

May, 2013, 4
June, 2013, 16
July, 2013, 64
January, 2014, 26,2144

How is it correct to multiply by 4 when each member is recruiting 3 new members each month? I would like to understand this better for future reference.

Thank you!

You're not tripling the number of members, you're adding new members, so you need addition, not multiplication.

_________________
(\ /)
(O.o)
(> <)
This is Bunny. Copy Bunny into your signature to help him on his way to world domination

End Apr: 1
End May: 4
1*4 = 4

_________________
I'm not prejudiced...I hate everybody equally!

Yes, effectively 1 becomes 4 each time.

_________________
(\ /)
(O.o)
(> <)
This is Bunny. Copy Bunny into your signature to help him on his way to world domination