In a 1.5 kg mixture of sand and iron, 30% is iron. How much sand needs to be added so that the proportion of iron becomes 15%?
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Great question!
Thankss
wait, answer is 1.5kg? I got 1500gms which is the same thing lol. took me a sec to realize D and A aren't close
same, i almost picked A because it was in grams and the others were kg. classic unit trap
the iron amount never changes, that's the key. just keep it fixed and figure out what total gives you 15%. pretty standard mixture setup
ohh that makes it way simpler than what i was doing. thanks!
this one felt easy for a 505-555. once you set up the iron stays constant its like two lines of math
agreed, definitely on the friendlier side
What it tests
Your ability to reason about weighted averages and the composition of mixtures.
Common trap
Averaging the percentages of two solutions without weighting by their volumes.