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Hello @ervin-lemark, this is Direct Anual Interest. So it would be:

(20% / 12months) * 3 months = 5%
600 + 5% = 630

Here is a table of what each investor would receive:

@lukestokes 210 Steem
@kingscrown 63 Steem
@ervin-lemark 105 Steem
@chitty 252 Steem

OK, got it. Thanks for the formula and the explanation.

Not that I am into big money here. Just that the rules are clear :)

Have a great weekend!