Jane bought a number of books at an average price of $8. If she decides to buy another book which cost $18, the average price of all the books will become $10. Find the number of books she bought?
A number of books at an average price of $8. Another book which cost $18, the average price of all the books will become $10.
Average price increases from $8 to $10.
10 – 8 = 2
Price of additional book is $10 (18 – 8) more than original average ($8).
18 – 8 = 10
Final number of books
10 ÷ 2 = 5
Original number of books. [Note: If she decides to buy another book.. - just an assumption.]
5 - 1 = 4 books
Original number of books. [Note: If she decides to buy another book.. - just an assumption.]
5 - 1 = 4 books
Jane bought 4 books.
Alternative method
10 – 8 = 2
Price of additional book is $8 (18 – 10) more than final average ($10).
18 – 8 = 10
The additional $10 is spread over the original number of books, $2 each to increase their average from $8 to $10. [Note: If she decides to buy another book.. - just an assumption.]
8 ÷ 2 = 4 books
Jane bought 4 books.
Jane bought 4 books.
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