AMC 8 Daily Practice Round 11

Complete problem set with solutions and individual problem pages

Problem 7 Easy

To increase the concentration of a 40-kilogram salt solution from 18\% to 20\%, how much water needs to be evaporated?

  • A.

    6 kg

  • B.

    5 kg

  • C.

    4 kg

  • D.

    3 kg

  • E.

    2.5 kg

Answer:C

The amount of salt in the solution remains unchanged before and after evaporation. Let x kilograms of water be evaporated. Then, the equation is:

40 \times 18\% = (40 - x) \times 20\%.

Solving for x, we get:

x = 4.

Thus, the amount of water that needs to be evaporated is \textbf{4 kg}.

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