Coffee beans lose 12.5% of their weight during roasting. in order to obtain 252 kg of roasted coffee beans, how many kg of unroasted beans must be used

We know that 252 kg of orasted coffee beans is 100% - 12.5% = 87.5% of the amount of unroasted beans, so we can write it down as:

252 = 87.5% of x
252 = 87.5/100 * x
252 = 875/1000x
252 = 175/200x
252 = 35/40x
252 = 7/8x                   / * 8 (both sides)
2016 = 7x                    / ÷ 7 (both sides)
x = 288 [kg]

We'll need to use 288 kg of unroasted coffee beans in order to obtain 252 kg of roasted beans.

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