Question 1205542
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Let x be the cost in dollars of each book.<br>
Alana bought 4 books, costing a total of 4x dollars; Petra bought 2, costing 2x dollars.  Together they spent 4x+2x = 6x dollars.<br>
Angus bought 16 books, costing a total of 32x dollars, but got a $15 discount, so the total he paid was 32x-15 dollars.<br>
The amount Angus spent was $5 more than Alana and Petra together:<br>
16x-15 = 6x+5
10x = 20
x = 2<br>
ANSWER: the cost of each book was $2<br>