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Question

Mdm Tang bought a number of bowls at an average price of $9. After she decided to buy another 12 bowls which cost $7 each, the average price became $7.50. Find the total number of bowls she bought at first.
How to do?
Tks

Answer

If Mdm Tang bought u bowls at average price of $9, the total amount she paid was 9u.

After she bought 12 bowls at 7 dollars,

the new average = 7.5 = ( 12 * 7 + 9u ) /( 12 + u )            multiply both sides by 12 + u

7.5( 12 + u )  = 84 + 9u

90 + 7.5u = 84 + 9u

1.5u = 8

u = 4

She bought 4 bowls at first.

Check : 36 + 84 = 120

120/ 16 = 7.5 Checked

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