Robert mott strength of material chapter8 problem 11 can you

Robert mott strength of material chapter8 problem 11 can you please tell me why the thickness is taken as 2 inches in the last step... If I look at the diagram the thickness is 1 inch...what procedure should I follow to ascertain the thickness....

Solution

the reason for that is that as we go further with the stresses with respect to thickness.. the thickness increases double the rate as stress increases. So, the scale is taken 2inches in the last step. I have an older version of the textbook with me.if you could post the link of pic of the graph in the comment box, i would explain it to you for sure.