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Lesson plan Grade 3 Math

Talcott Flats Well Field: A Grade 3 Two-Step and Estimate Lesson

A 50-minute grade 3 lesson where students round to the nearest ten to estimate, then solve two-step problems about water pumped from four wells in a fictional town.

Objectives

  1. Students will round three-digit numbers to the nearest ten to estimate a sum.
  2. Students will solve two-step word problems and write an equation with a letter for the unknown.
  3. Students will use an estimate to judge whether an exact answer is reasonable.

Vocabulary

Key words: well, estimate, round, two-step, reasonable

Teacher overview

Many small towns take their drinking water from a group of wells drilled into an aquifer, and a crew checks how much each well pumps in one minute. The town of Talcott Flats in this lesson is fictional, and every number in the well log was invented for the lesson rather than drawn from a real utility. Students round the one-minute well readings to the nearest ten, add the rounded numbers to make an estimate, then find the exact answer and compare the two. The misconception this lesson targets is the habit of stopping after the first step of a two-step problem, as when a student correctly multiplies to find a total and then hands in that total as the final answer without subtracting what was used.

Procedure

Hook (5 min): Write 128 and 214 on the board and ask students to say, without adding, whether the total will be closer to 300 or closer to 400. Take three explanations. Do not confirm an answer yet.

Direct instruction (12 min): Introduce the setting: Talcott Flats has four wells, and the crew writes down the liters each well pumps. Model rounding 128 and 214 to the nearest ten on an open number line, marking the two tens each number falls between and deciding which is nearer. Add the rounded numbers to get the estimate, then add the exact numbers, and put the two results side by side so students see how close they are. Then model one two-step problem all the way through: a well fills 4 tanks of 30 liters, so that is 4 × 30 = 120 liters, and the crew then uses 50 liters, so 120 − 50 = 70 liters are left. Write the equation with a letter for the unknown and circle the second step.

Guided practice (13 min): Students work handout items 1 and 2 with a partner. Both partners round on their own number line, compare the two estimates, and only then add the exact numbers. Then work item 3 as a class, having a student come up and label which part of the equation is step one and which is step two.

Independent practice (15 min): Students complete handout items 4 and 5 alone. As they work, ask three students at random to point to the second step in their own written equation. This is the formative check: if fewer than two-thirds of the class can point to a second step, pause the room and re-model item 3 before letting students continue.

Closure (5 min): Students answer handout item 6 as an exit ticket. Read the pile quickly and note which students used an estimate rather than recomputing, since that is the reasoning move the next lesson builds on.

Talcott Flats Well Field: A Grade 3 Two-Step and Estimate Lesson — Grade 3 Math
Name: ____________________________ Date: ______________

Student Handout

Talcott Flats has four wells. The crew writes down how many liters each well pumps.

  1. On Monday, Well 1 pumped 128 liters in one minute and Well 2 pumped 214 liters in one minute. Round each number to the nearest ten. Then add the two rounded numbers to estimate the total.
  2. Now add the two exact numbers from item 1. How many liters did Well 1 and Well 2 pump together in that minute?
  3. Well 3 filled 5 tanks. Each tank holds 30 liters. The crew then used 60 liters from those tanks. How many liters are left?
  4. Well 4 pumped 320 liters. The crew sent 145 liters to the school. Then the crew sent 90 liters to the park. How many liters are left?
  5. The crew has 8 rows of spare pipe. Each row holds 4 pipes. The crew takes away 7 pipes. How many pipes are left?
  6. A worker says the answer to item 4 must be more than 200 liters. Use rounding to explain whether the worker is right.

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: 340 liters.
    Rounding to the nearest ten gives 128 to 130 and 214 to 210, and 130 + 210 = 340 liters as the estimate.
  2. Answer: 342 liters.
    Adding the exact numbers gives 128 + 214 = 342 liters, which is very close to the estimate of 340.
  3. Answer: 90 liters.
    Step one is 5 × 30 = 150 liters in the tanks. Step two is 150 − 60 = 90 liters left. As an equation, 5 × 30 − 60 = n, and n = 90.
  4. Answer: 85 liters.
    Step one is 320 − 145 = 175 liters after the school delivery. Step two is 175 − 90 = 85 liters after the park delivery. As an equation, 320 − 145 − 90 = n, and n = 85.
  5. Answer: 25 pipes.
    Step one is 8 × 4 = 32 pipes on the rows. Step two is 32 − 7 = 25 pipes left. As an equation, 8 × 4 − 7 = n, and n = 25.
  6. Answer: No.
    Rounding gives 145 to about 150 and 90 stays 90, and 320 − 150 − 90 is about 80 liters, so the answer has to be far below 200 liters. The worker is not right.

Differentiation

Support

Give students a pre-drawn open number line for item 1 with the tens already labeled, so the rounding decision is a matter of marking a point rather than building the line. Provide a two-box organizer labeled "Step 1" and "Step 2" for items 3, 4, and 5, and let students write one equation in each box before combining them. Counters or base-ten blocks help for the multiplication step.

Extension

Ask students to change one number in item 4 so that the answer lands between 100 and 150 liters, then prove the new answer with both an estimate and an exact calculation. Have them write a two-step well problem of their own in which the estimate and the exact answer differ by less than 5 liters, and explain what made the two results so close.

ELL supports

Pre-teach "well," "pump," "round," and "estimate" using a simple cross-section sketch of a well drawing water from the ground. Post the sentence frames "First I ___. Then I ___." for the two-step items, and "My estimate is ___, so the answer should be about ___." for items 1 and 6. Allow students to show the two steps with labeled drawings before writing the equation.