<PRE><B>Question 1168057</B>
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His income from selling the books is not linear; but it is always increasing.  So, as the other tutor suggests, the easiest way to solve the problem is just to make a reasonable guess and work from there.&lt;br&gt;
He gets $1200 for selling 100 books, not counting the bonuses.  Since that is a bit less than the total he makes including bonuses, let&#39;s find his total income, including bonuses, for selling 100 books.&lt;br&gt;
$12 * 100 = $1200  ($12 for each book)
$5 * 10 = $50  ($5 bonus for each group of 10 books)
$50 *1 = $50  ($50 bonus for selling 100 books)&lt;br&gt;
Total: $1300&lt;br&gt;
Since he made $1372, we know the number of books he sold was more than 100.  So our guess of 100 books was a good starting place.&lt;br&gt;
The difference between the $1372 he made and the $1300 he makes for selling 100 books is $72.&lt;br&gt;
That is what he makes for selling $72/$12 = 6 books; and he won&#39;t get any additional bonuses for selling 6 more books after the first 100.&lt;br&gt;
So the number of books he sold is 106.&lt;br&gt;
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