Calculate retained particle count

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or browser document; an ordinary calculator is optional.
• Rule: Retained count equals input particle count minus output particle count. Formula: a-b. Variable key: a = input particles, b = output particles
• Distinct worked inputs and result: A distinct record has 24 input particles and 6 output: 24-6=18 retained.
• Assessment case 1: Supplied case 1: input particles=40; output particles=10, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?
• Assessment case 2: Supplied case 2: input particles=50; output particles=15, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?
• Assessment case 3: Supplied case 3: input particles=30; output particles=5, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?
• Assessment case 4: Supplied case 4: input particles=60; output particles=20, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?
• Assessment case 5: Supplied case 5: input particles=80; output particles=25, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?
• Assessment case 6: Supplied case 6: input particles=100; output particles=30, using the explicitly named quantities. Retained count equals input particle count minus output particle count. What result follows?

Learn the idea

Use a count before and after a supplied filter. This checks the listed particle category only. Smaller particles or dissolved contaminants can remain even when the count falls.

Retained count equals input particle count minus output particle count. The formula in the supplied model is a-b. Variable key: a = input particles, b = output particles. Count the same particle category at input and output. Do not equate fewer particles with drinking safety.

A distinct record has 24 input particles and 6 output: 24-6=18 retained. Keep output counts in the record. Track the quantity and unit before calculating. Explain the meaning of a positive, negative or fractional result when relevant. A numerical answer supports the stated model calculation; broader claims require the additional measurements and assumptions described here.

1. Name the measured quantities and their units before substituting values.
2. Write the stated rule and use the variable key to match each symbol to its explicitly named quantity.
3. Calculate each supplied case separately, keeping intermediate arithmetic and the result unit.
4. Explain the result in context and identify the assumption that would invalidate direct use of the rule.

Check your reasoning

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Take it further

Changed-input task: use the same stated model with input particles=41; output particles=10. Expected result: 31 particles. Explain what changes and keep this assumption: Keep output counts in the record.

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