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Math problem set Grade 5 Science

Ashcott's Drain Screens: A Grade 5 Fair Test Problem Set

A grade 5 problem set weighing debris and drain times from four storm drain screen trials in a fictional town, including one trial that was not a fair test.

Objectives

  1. Students will subtract decimals to hundredths to find how much debris passed through each screen.
  2. Students will compare four trial results on both debris caught and drain time.
  3. Students will identify the trial that was not a fair test and explain why its result cannot be trusted.

Vocabulary

Storm drain
A storm drain is the grate at the edge of a street that swallows rainwater and sends it through pipes to the nearest creek or river. That water is usually not treated, so only rain belongs down the drain.

Also: fair test, trial, debris, screen

Teacher overview

Ashcott is a fictional town whose Mill Street storm drain clogs with leaves and grit every autumn, and the street floods when it does. The public works crew tested four screens that fit inside the drain opening, pouring the same amount of water and the same weighed mix of debris through each one, then recording both the debris the screen held back and the time the water took to drain through. The set is written to correct the assumption that the screen catching the most debris is automatically the best choice, because a screen that catches too much also slows the water enough to send a storm back onto the street. Problems 7 through 10 target a second error, which is trusting a result from a trial in which two conditions changed at once. The fourth screen was tested with less water than the other three, and its apparent advantage disappears once the crew repeats the trial with the same amount of water the other three received.

Ashcott's Drain Screens: A Grade 5 Fair Test Problem Set — Grade 5 Science
Name: ____________________________ Date: ______________

Problems

Ashcott is a fictional town. Leaves and grit clog the storm drain on Mill Street, and the street floods. The crew tested four screens that sit inside the drain opening.

In each test the crew poured 6 liters of water into the drain. The water carried a mix of leaves and grit that weighed 30.00 grams. The crew weighed the debris each screen held back. They also timed how long the water took to drain through.

Here are the crew's results.

  • Screen 1: openings 12 millimeters wide. Held back 6.45 grams. Drained in 17.60 seconds.
  • Screen 2: openings 9 millimeters wide. Held back 14.80 grams. Drained in 24.50 seconds.
  • Screen 3: openings 6 millimeters wide. Held back 22.35 grams. Drained in 41.75 seconds.
  • Screen 4: openings 6 millimeters wide, set in a taller basket. Held back 24.60 grams. Drained in 39.40 seconds. This test used 5 liters of water, not 6.
  1. Screen 1 held back 6.45 grams of the 30.00 grams of debris. How many grams went on down the drain?
  2. Screen 3 held back 22.35 grams of the 30.00 grams of debris. How many grams went on down the drain?
  3. How many more grams of debris did Screen 3 hold back than Screen 2?
  4. How many more seconds did Screen 3 take to drain than Screen 1?
  5. Mill Street has 4 storm drains. Suppose every drain used a Screen 2, and each one held back 14.80 grams in a storm. How many grams would the four screens hold back in all?
  6. Water left standing in the street starts to flood it, so the crew wants the water gone in less than 30 seconds. How many of the four screens drained in less than 30 seconds?
  7. The Screen 4 test used 5 liters of water. The other three tests each used 6 liters. How many liters less did the Screen 4 test use?
  8. In a fair test, everything stays the same except the one thing being tested. How many of the four tests used 6 liters of water?
  9. Screen 3 and Screen 4 have openings the same width. Only the basket height is different. Screen 3 held back 22.35 grams and Screen 4 held back 24.60 grams. What is the difference between those two weights?
  10. The crew ran the Screen 4 test again with the full 6 liters of water. This time Screen 4 held back 21.90 grams. Screen 3 held back 22.35 grams with 6 liters. How many more grams did Screen 3 hold back?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 23.55 grams. The debris mix weighed 30.00 grams and the screen held back 6.45 grams, so 30.00 minus 6.45 leaves 23.55 grams that washed on into the drain.
  2. Answer: 7.65 grams. Subtract the same way: 30.00 minus 22.35 leaves 7.65 grams. The narrower openings let far less debris through than Screen 1 did.
  3. Answer: 7.55 grams. Line up the decimal points and subtract: 22.35 minus 14.80 is 7.55 grams. Narrowing the openings from 9 millimeters to 6 millimeters caught this much more.
  4. Answer: 24.15 seconds. Subtract the two drain times: 41.75 minus 17.60 is 24.15 seconds. The screen that caught the most debris was also the slowest to let the storm through, which is the trade-off the crew has to weigh.
  5. Answer: 59.20 grams. Multiply the weight one screen held back by the number of drains: 14.80 times 4 is 59.20 grams for the whole street.
  6. Answer: 2 screens. Compare each drain time with 30 seconds. Screen 1 at 17.60 seconds and Screen 2 at 24.50 seconds are both under 30, while Screen 3 at 41.75 seconds and Screen 4 at 39.40 seconds are both over it.
  7. Answer: 1 liter. Subtract the two amounts: 6 minus 5 is 1 liter less water in the Screen 4 test than in the others.
  8. Answer: 3 tests. Screens 1, 2, and 3 each received 6 liters. Only the Screen 4 test differed, so it changed two things at once, the basket height and the water amount.
  9. Answer: 2.25 grams. Subtract: 24.60 minus 22.35 is 2.25 grams. Screen 4 looks better by this much, yet its test used less water, so the comparison does not show what the taller basket did.
  10. Answer: 0.45 grams. Subtract: 22.35 minus 21.90 is 0.45 grams. With both tests at 6 liters, Screen 3 held back more than Screen 4, so the taller basket did not improve the screen. The 2.25 gram lead in problem 9 came from the smaller amount of water, not from the design.

Differentiation

Support

Give these students the four results copied into a two-column chart, one column for grams held back and one for drain time, so they are not searching the paragraph for each number. Provide a place-value grid with the decimal points already aligned for problems 1 through 4, and write 30.00 at the top of the grid so the two zeros in the hundredths place are visible before they subtract.

Extension

Ask these students to suppose the crew tests a fifth screen with openings 3 millimeters wide, predict both of its numbers, and explain the trade-off their prediction assumes. Then have them write the one change that would have made the Screen 4 trial fair, and explain why that change matters more than any of the arithmetic in the set.

ELL supports

Preteach four phrases with pictures: "held back," "drained through," "debris," and "fair test." A short demonstration with a kitchen strainer and shredded paper makes "held back" and "drained through" concrete in under a minute. Offer sentence frames such as "Screen ___ held back ___ grams" and "The Screen 4 test was not fair because ___."

Extensions

Have students plan the next round of testing on paper, listing what must stay the same and naming the one thing they would change. Students can also suppose Ashcott installs Screen 2 on Mill Street and write what the crew should measure after the first storm to find out whether the choice worked, which turns the classroom comparison into a maintenance plan the town could follow.