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Material cost of a web camera is five eighth of 
total cost and labour cost is one third of material cost.
If labour cost is $15 what is the total cost of the web camera.
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1. The labor costs 1/3 of the material cost; and the labor costs $15.
Hence, the material cost 3 times $15, i.e. 45 dollars.
2. The material costs 5/8 of the total cost; from the other side, it costs $45.
Hence, 1/8 of the total cost is 1/5 of $45, i.e. $9.
Then the total cost of the web-camera is 8 times $9, i.e. 8*9 = 72 dollars.
Answer. The total cost of the web-camera is 72 dollars.
Easy mental solution.
