James has $1100 invested at r% and $900 invested at (r+1)%. if his annual income on these two investments is $99, find r.

First, we need to set up an equation. Some number out of 100 (percent) times $1100 plus the same percent plus 1 times $900 will give us $99.

(r/100) x 1100 + ((r+1)/100) x 900 = 99

(r x 1100)/100 + ((r+1) x 900)/100 = 99

11r + 9(r+1) = 99

20r + 9 = 99

20r = 90

20r/20 = 90/20

r=90/20 = 9/2

r  = 4.5%

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