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Mixtures and solutions – practice for Years 8–9

Sample questions on Mixtures and solutions with the right answer and a worked solution, from easy to hard. In the Pickles Academy app a child gets new questions of the same kind every time, so they can't just learn the answers by heart.

Subject
Maths
Year
Years 8–9
Curriculum area
Relationships, functions and data

Question types: Percentages in mixtures

Rule: Mixtures and solutions

Concentration = amount of the substance ÷ mass of the whole solution (× 100%).

When diluting or mixing, the amount of the substance (salt, sugar) doesn’t change: work it out separately.

Example: 80 g of sugar in 320 g of water: 80 ÷ 400 = 0.2 = 20%

Watch out: Divide by the whole solution (water + substance), not just the water: 80 ÷ 320 is wrong.

Sample questions

  1. Question 1 Easy

    125 g of sugar is dissolved in 375 g of water. What percentage of the solution is sugar?

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    Answer: 25%

    How it works: The solution weighs 375 + 125 = 500 g; 125 ÷ 500 = 0.25 = 25%

  2. Question 2 Normal

    We mix 4 kg of a solution that is 25% salt with 6 kg of a solution that is 30% salt. What percentage of the mixture is salt?

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    Answer: 28%

    How it works: Salt: 4 × 0.25 + 6 × 0.3 = 2.8 kg; 2.8 ÷ 10 = 0.28 = 28%

  3. Question 3 Hard

    We have 9 kg of a solution that is 40% salt. How many kilograms of water must we add so that the solution is 20% salt?

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    Answer: 9 kg

    How it works: Salt: 0.4 × 9 = 3.6 kg; it makes up 20% of the new solution: 3.6 ÷ 0.2 = 18 kg; add 18 − 9 = 9 kg of water

Related topics

All Maths topics

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