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04 Feb 2025, 11:09
Kudos
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For mixture problems, it is easier to focus on the thing that is not changing.
So, the initial mixture had 7kg humus and by removing x kg, we remove 0.7x which leaves 5kg, essentially we are removing 2kg of humus
0.7x = 2
x=20/7 = 2.9
So, the initial mixture had 7kg humus and by removing x kg, we remove 0.7x which leaves 5kg, essentially we are removing 2kg of humus
0.7x = 2
x=20/7 = 2.9
AnkurGMAT20
16 Feb 2026, 12:53
Kudos
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AnkurGMAT20
An alternate approach is to PLUG IN THE ANSWERS, which represent the amount of pure sand used to replace part of the original mixture.
When the correct answer is plugged in, the resulting amount of sand will sum to 5 kilograms (50% of the 10-kilogram total).
D: 4 kilograms pure sand, implying 6 kilograms of the original mixture
Since the original mixture is 30% sand, we get:
Total sand = 4 + (0.3)(6) = 5.8
Too much sand.
B: 2.9 kilograms pure sand, implying 7.1 kilograms of the original mixture
Since the original mixture is 30% sand, we get:
Total sand = 2.9 + (0.3)(7.1) ≈ 2.9 + 2.1 = 5
Success!
