Question 1115859
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The combined weight of the first two is 70% of the total weight, so the weight of the third chemical is 30% of the total.<br>
If the ratio of the second and third chemicals is 4:3 and the third chemical is 30% of the total weight, then the second chemical is 40% of the total weight.<br>
If the second chemical is 40% of the total weight and the third is 30% of the total, then the first is 30% of the total.<br>
So 30% first chemical, 40% second, and 30% third.  With a total weight of 700 kg, you need
210 kg of first
280 kg is second
210 kg of third