55% is Cu and FE so 45% is zinc
.45 *720 = 324 grams
That is assuming this is a MATH, not a Chemistry problem. If it were Chemistry they might be looking at 1/4 of the molecules are Cu, not 1/4 of the mass.
An alloy is made up of 25% copper, 30% iron an rest being zinc. Find the mass of zinc in 720 gm of the alloy
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