The Life Starter
Sign up
Grade 4 · lesson 3 of 4

Compare Useful Outputs Fairly

Use equal inputs to compare outputs for one stated purpose.

Download the grade pack

Supplied materials

  • Use the supplied fictional observations or model. Paper and pencil are optional; spoken answers are welcome. No equipment or real experiment is needed.

Learn the idea

To compare two lighting models fairly, keep the energy input and time interval alike. Then ask how much of that input serves the lighting goal. Our fictional lamp A receives 40 units and sends 10 as light and 30 as thermal energy. Lamp B receives 40 units and sends 16 as light and 24 as thermal energy.

Both ledgers conserve the same input, but B provides 6 more light units in this simplified comparison. A useful output depends on the purpose: thermal output might serve a heating task, but it is not the desired sign-lighting output here. These numbers alone do not describe color, durability, or the price of a real lamp.

  1. Check that A and B each account for 40 units.
  2. Circle the light outputs, 10 and 16.
  3. Subtract 10 from 16 to find the useful-output difference.
  4. Choose for the lighting goal and state one detail the model does not supply.
Worked example

See the method in action

A: 10 + 30 = 40. B: 16 + 24 = 40. B transfers 16 − 10 = 6 additional light units for the same input; it also transfers fewer thermal units.

Your turn

Check your reasoning

Your answer is temporary and is not saved to an account. Download your current answer before leaving or reloading. Written work on paper or in another app stays in your own file.

Which conclusion fits the equal-input model?

Feedback appears here after you check. This is practice, not a graded school assessment.

See the answer and explanation

B provides 6 more light units for this goal.

The inputs match and B’s light output exceeds A’s by 6 units. Both total outputs still equal 40.

Take it further

Replace B’s ledger with input 80 units, light output 20 units, thermal output 60 units, and no storage change. A’s useful share is 10/40 = one quarter and B’s is 20/80 = one quarter. B’s larger light amount no longer shows a larger useful fraction.

Nothing here is saved to an account or sent to a teacher. The answer download includes your current choice and any checked feedback.

Check the subject sources

These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.