Bonnie and Calvin start reading the same book. Bonnie read 10 more pages a day more than Calvin, Calvin finishes the book in 12 days, Bonnie finishes in 10 days.  How many pages a day did Calvin read?

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The total numbers of pages read by them both can be obtained by multiplying the rate of how many pages they read per day times the amount of days it took for them to read the book.  This is essentially a D = RT problem where the D is the total pages in the book, the R is how many pages they read per day, and the T is how many days it takes them to finish.  Since they both are reading the same book, we know the D's are the same so our equation can be D(Calvin) = D(Bonnie).  Then we use D = RT to get those expressions for those D's to use in that equation.Since they are asking for Calvin's pages per day, let's call that x.  His time was 12 days which makes his D: 12x.Bonnie reads 10 more pages a day than him: x + 10.  Her time was 10 days.  Making her D: 10(x + 10).Set these D's equal to each other and solve for x.12x = 10(x + 10)12x = 10x + 1002x = 100x = 50.Calvin reads 50 pages a day.  We can also now use this information to know how many pages the book has 12x = 12(50) = 600