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Math problem set Grade 3 Math

South Fork Watershed's Rainfall Totals: A Grade 3 Problem Set

A grade 3 math set where students add, subtract, and halve four months of a fictional watershed's rainfall to track how much water recharges the ground.

Objectives

  1. Students will add and subtract three-digit rainfall totals from a watershed's monthly record.
  2. Students will find half of a measured amount to model how rain splits between soaking into the ground and flowing into a stream.
  3. Students will check a two-part answer by confirming that both parts add back up to the original total.

Vocabulary

Watershed
A watershed is all the land where rain that falls will drain to the same stream, river, or lake. Everyone lives in a watershed, no matter how far from the water they live.
Groundwater
Groundwater is water that has soaked into the ground and fills the spaces between soil particles and cracks in rock underground. It is a large underground source of fresh water that wells and springs draw from.
Recharge
Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.
Aquifer
An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.

Teacher overview

A monitoring station in the fictional South Fork Watershed records how many millimeters of rain fall each month over a four-month season. Not all of that rain stays on the surface: some soaks down through the soil to refill the underground water supply, called an aquifer, in a process called recharge, while the rest flows across the land into the stream. In real watersheds some rain also evaporates or is taken up by plants; this set leaves that part out to keep the numbers simple. This set uses the watershed's rainfall record for addition, subtraction, and simple halving practice. A common misconception is that all of the rain that falls soaks into the ground; problems 5 through 8 show that only part of it recharges the aquifer.

South Fork Watershed's Rainfall Totals: A Grade 3 Problem Set — Grade 3 Math
Name: ____________________________ Date: ______________

Problems

The South Fork Watershed recorded rain each month: March, 85 mm; April, 120 mm; May, 95 mm; June, 140 mm.

  1. Add March and April.
  2. Add May and June.
  3. Add your answers from problems 1 and 2. This is the four-month total.
  4. Find the month with the most rain. Find the month with the least. What is the difference?
  5. About half of April's rain soaks into the ground to recharge the aquifer. April had 120 mm. How many mm soaked in?
  6. About half of June's rain soaks into the ground too. June had 140 mm. How many mm soaked in?
  7. Add your answers from problems 5 and 6. This is the total recharge for April and June.
  8. Challenge. The other half of the rain flows into the stream instead. Find the stream total for April and June. Then add it to your answer from problem 7. Does the sum equal 120 + 140?

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: 205 mm. 85 + 120 = 205.
  2. Answer: 235 mm. 95 + 140 = 235.
  3. Answer: 440 mm. 205 + 235 = 440.
  4. Answer: 55 mm. June had the most rain (140 mm) and March had the least (85 mm). 140 − 85 = 55.
  5. Answer: 60 mm. Half of 120 is 120 ÷ 2 = 60.
  6. Answer: 70 mm. Half of 140 is 140 ÷ 2 = 70.
  7. Answer: 130 mm. 60 + 70 = 130.
  8. Answer: 130 mm. The stream amount is also 60 mm from April (120 − 60) plus 70 mm from June (140 − 70), which equals 130 mm. Checking the work: 130 mm (recharge) + 130 mm (stream) = 260 mm, which matches April and June's combined rainfall of 120 + 140 = 260 mm.

Differentiation

Support (below grade level)

Provide a printed place-value chart for the addition and subtraction steps, and give students the halving fact "120 ÷ 2 = 60" already worked out as a model before they find half of 140 on their own in problem 6.

Extension (above grade level)

Ask students to calculate how many millimeters would recharge the aquifer if May's 95 mm followed the same "about half soaks in" pattern, and to explain why 95 does not split into two whole, equal numbers the way 120 and 140 do.

ELL supports

Pre-teach "watershed," "aquifer," and "recharge" using a simple side-view drawing that shows rain falling, some soaking down into a labeled underground water layer, and some flowing along the surface into a stream. Provide a sentence frame for problem 4: "___ had the most rain and ___ had the least, a difference of ___ millimeters."