alltimeacheiver wrote:The cost C of manufacturing a certain product can be estimated by the formula C = 0.03rs(t^2) where r and s are the amounts, in pounds of the two major ingredients and t is the production time, in hours. If r is increased by 50 percent, s in increased by 20 percent, and t is decreased by 30 percent, by approximately what percent will the estimated cost of manufacturing the product change?
40% increase
12% increase
4% increase
12% decrease
24% decrease
I have gone mad with comples calculations. pls suggest good method
Ignore the .03, since it will be common both to the original cost and to the changed cost and will not affect the change in percentage.
We can plug in values.
Let r=10, s=10, and t=10.
Then rs(t^2) = 10*10*(10^2) = 10,000.
New r increased by 50% = 15.
New s increased by 20% = 12.
New t decreased by 30% = 7.
New rs(t^2) = 15*12(7^2) = 180*49 ≈ 180*50 ≈ 9,000.
10,000 to 9,000 = 10% decrease.
Since when we calculated 9,000 we rounded up, the actual decrease will be just a bit more than 10%.
The correct answer is
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