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Worksheet Grade 4 Math

Marrowick Cleaning Ponds: Multiplying Microbe Feeding Batches

A grade 4 worksheet at a fictional water cleaning pond, where students multiply paddle turns, tray scoops, and daily barrel totals and interpret a remainder.

Objectives

  1. Students will multiply two two-digit numbers and a four-digit number by a one-digit number to find totals at a water cleaning pond.
  2. Students will solve a two-step word problem and interpret a remainder as an extra cart trip.
  3. Students will explain in writing why an estimate is or is not close to a computed total.

Vocabulary

Key words: microbe, starter mix, paddle wheel, remainder, estimate

Teacher overview

Marrowick is a fictional town that cleans its used water in three shallow ponds instead of a tank plant. Microbes, which are living things too small to see without a microscope, eat the waste in the water, and slow paddle wheels stir air into the ponds so the microbes keep working. This worksheet follows one week at the ponds, counting paddle turns, measuring out the starter mix that feeds the microbes, and totaling the barrels of water the ponds clean. Watch for students who answer item 7 with 28 trips: two trays are left after the twenty-eighth cart load, and those two trays still need a trip of their own.

Marrowick Cleaning Ponds: Multiplying Microbe Feeding Batches — Grade 4 Math
Name: ____________________________ Date: ______________

Student Worksheet

  1. Pond A has 3 paddle wheels. Each wheel turns 26 times each minute. How many turns do the 3 wheels make together in one minute?

  2. One paddle wheel turns 26 times each minute. How many turns does that one wheel make in 45 minutes?

  3. A tray of starter mix holds 32 scoops. A worker fills 7 trays on Monday. How many scoops does she use?

  4. In one month the plant fills 48 trays. Each tray holds 32 scoops. How many scoops is that?

  5. The three ponds clean 2,150 barrels of used water each day. How many barrels do they clean in 4 days?

  6. A worker checks each of the 3 ponds for 15 minutes. After the checks she writes notes for 20 minutes. How many minutes does the whole job take?

  7. The plant must move 226 empty trays to the wash room. One cart holds 8 trays. How many cart trips does it take to move all the trays?

  8. Look at your answer to item 7. Explain why the last cart trip is not a full cart.

  9. The three ponds clean 2,150 barrels of used water each day. How many barrels do they clean in 5 days?

  10. A worker guessed that 5 days would be close to 10,000 barrels. Use your answer to item 9 to tell whether that guess was close, and explain how you know.

  11. The paddle wheels stir air into the water so the microbes can work. Explain what might happen to the cleaning if the wheels stopped for a whole day.

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: 78 turns.
    Three wheels each turn 26 times, so 26 × 3 = 78 turns in one minute. Students may add 26 + 26 + 26 instead.

  2. Answer: 1,170 turns.
    26 × 45. Split 45 into 40 + 5. Then 26 × 40 = 1,040 and 26 × 5 = 130. Adding the two partial products gives 1,040 + 130 = 1,170 turns.

  3. Answer: 224 scoops.
    32 × 7. Split 32 into 30 + 2. Then 30 × 7 = 210 and 2 × 7 = 14, so 210 + 14 = 224 scoops.

  4. Answer: 1,536 scoops.
    32 × 48. Split 48 into 40 + 8. Then 32 × 40 = 1,280 and 32 × 8 = 256, so 1,280 + 256 = 1,536 scoops.

  5. Answer: 8,600 barrels.
    2,150 × 4. Split 2,150 into 2,000 + 150. Then 2,000 × 4 = 8,000 and 150 × 4 = 600, so 8,000 + 600 = 8,600 barrels.

  6. Answer: 65 minutes.
    Three pond checks take 15 × 3 = 45 minutes. Adding the 20 minutes of note writing gives 45 + 20 = 65 minutes.

  7. Answer: 29 trips.
    226 ÷ 8. Eight goes into 226 twenty-eight times because 8 × 28 = 224, leaving 2 trays. Those 2 trays still need a cart, so the crew makes 28 full trips plus 1 more, which is 29 trips.

  8. Answer: Two trays are left after the full loads, so the last cart carries only 2 trays instead of 8.
    Students should connect the remainder of 2 from item 7 to the size of the last load. A response that says the remainder is thrown away has misread the situation.

  9. Answer: 10,750 barrels.
    2,150 × 5. Split 2,150 into 2,000 + 150. Then 2,000 × 5 = 10,000 and 150 × 5 = 750, so 10,000 + 750 = 10,750 barrels.

  10. Answer: The guess was close, because 10,750 is only 750 more than 10,000.
    Accept any answer that compares 10,750 with 10,000 and names the difference of 750 barrels. Students who rounded 2,150 to 2,000 first and got 10,000 should be praised for a sound estimate.

  11. Answer: The microbes would get less air, so they would eat the waste more slowly and the water would leave the pond less clean.
    Accept any answer linking stopped paddles to less air and slower cleaning.

Differentiation

Support

Give students a partial-product box for items 2 and 4 with the two smaller multiplications already labeled, so the work becomes two easy products plus one addition. For item 7, offer counters or tally marks in groups of 8 so the leftover pair of trays is visible before the division is written.

Extension

Ask students to plan a fourth pond that would raise the daily total in item 5 to exactly 3,000 barrels, then write the multiplication that shows how many barrels the new pond must handle over 4 days.

ELL supports

Pre-teach "scoop," "tray," "cart trip," and "left over" with a simple labeled sketch of a cart holding eight trays. Provide the sentence frame: The plant needs ___ trips because 8 trays fit on one cart and ___ trays are left over.

Extensions

Have students write one more item for this worksheet using a paddle wheel that turns a different number of times each minute, trade papers with a partner, and check each other's multiplication with a partial-product drawing.