i have a hard time understanding the answer, can any one help?

Look at the Y axis. Its logarithmic, not linear. Notice how 100K is the same distance from 1 mil as 10 mil. Based on that, we can tell that half the distance on y axis means you cover about 1 tenth of the difference in 2 points. So the midpoint between 100,000 and 1 million is only (.10)(900000)+100000 = 190,000. The midpoint between 190,000 and 1 million is only (.10)(810000)+190000 = 271,000 270,000 is about the 10% line in 2012, so you can only say that John Stevensen will have 271,000 with 90% confidence. To get his target 630,000 you probably have to go to 70% or so.

FWIW this is a SUPER SUPER tricky bullcrap question. CFAI likes to make the exams tricky, but I canâ€™t imagine them doing something this diabolical on Saturday, so you can breathe easy.

thanks very much for the answer. one more question please, is there a way to do log calculation using our BAII Plus?