Worksheet Grade 7 Math
Moorhen Bend's Five Rain Gauges: A Grade 7 Intensity Worksheet
A grade 7 worksheet where students divide fractions of an inch by fractions of an hour to compare rainfall rates at a fictional town's five rain gauges.
Objectives
- Students will compute a rainfall rate in inches per hour from fractional amounts and times.
- Students will compare rainfall rates written as fractions and as decimals.
- Students will use a rate to predict rainfall over a longer or shorter time.
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: rain gauge, rainfall rate, unit rate, intensity
Teacher overview
Two storms can drop the same total rain and still put very different loads on a drainage system, because what floods a street is the rate at which rain arrives rather than the total depth. Utilities therefore record both the depth in a gauge and the length of time it took to collect, then divide to get inches per hour. This worksheet uses five gauges in the fictional town of Moorhen Bend, each reporting a fraction of an inch collected over a fraction of an hour. The predictable error is multiplying instead of dividing: a student who multiplies three-quarters of an inch by one-half hour reports three-eighths of an inch per hour, when dividing gives the correct 1.5 inches per hour.
Student Worksheet
Moorhen Bend is a fictional town with five rain gauges. Each gauge reports how much rain it caught and how long the rain took to fall.
Gauge 1 caught 3/4 inch in 1/2 hour.
Gauge 2 caught 1/2 inch in 1/4 hour.
Gauge 3 caught 5/8 inch in 3/4 hour.
Gauge 4 caught 1 1/4 inches in 1 1/2 hours.
Gauge 5 caught 7/8 inch in 5/8 hour.
- What is Gauge 1's rainfall rate, in inches per hour?
- What is Gauge 2's rainfall rate, in inches per hour?
- What is Gauge 3's rainfall rate, in inches per hour? Give a fraction.
- What is Gauge 4's rainfall rate, in inches per hour? Give a fraction.
- What is Gauge 5's rainfall rate, in inches per hour?
- Which gauge had the fastest rate?
- Two gauges had the same rate. Which two?
- Rain keeps falling at Gauge 1's rate for 2 1/2 hours. How many inches fall?
- At Gauge 3's rate, how many hours would it take to collect 2 inches?
- The storm drains in Moorhen Bend can carry rain falling up to 1 3/4 inches per hour. Which gauge recorded a rate above that?
- How much slower is Gauge 5's rate than Gauge 1's rate, in inches per hour?
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: 1.5 inches per hour.
Divide 3/4 by 1/2. Multiply 3/4 by 2 to get 3/2, which is 1.5 inches per hour. - Answer: 2 inches per hour.
Divide 1/2 by 1/4. Multiply 1/2 by 4 to get 2 inches per hour. - Answer: 5/6 inch per hour.
Divide 5/8 by 3/4. Multiply 5/8 by 4/3 to get 20/24, which reduces to 5/6, or about 0.83 inch per hour. - Answer: 5/6 inch per hour.
Rewrite the mixed numbers as 5/4 inch and 3/2 hours. Multiply 5/4 by 2/3 to get 10/12, which reduces to 5/6 inch per hour. - Answer: 1.4 inches per hour.
Divide 7/8 by 5/8. Multiply 7/8 by 8/5 to get 7/5, which is 1.4 inches per hour. - Answer: Gauge 2.
Its rate of 2 inches per hour is larger than the rates of 1.5, 5/6, and 1.4. - Answer: Gauge 3 and Gauge 4.
Both work out to 5/6 inch per hour, even though their depths and times look different. - Answer: 3.75 inches.
Multiply the rate by the time: 1.5 times 2 1/2 equals 1.5 times 2.5, which is 3.75 inches. - Answer: 2.4 hours.
Divide the depth by the rate: 2 divided by 5/6 is 2 times 6/5, which is 12/5, or 2.4 hours. - Answer: Gauge 2.
Its rate of 2 inches per hour is above 1 3/4, which is 1.75. Gauge 1 at 1.5 and Gauge 5 at 1.4 both stay below that line. - Answer: 0.1 inch per hour.
Subtract the two rates: 1.5 minus 1.4 equals 0.1 inch per hour.
Differentiation
Support
Give these students a worked card showing that dividing by a fraction means multiplying by its reciprocal, using a gauge that is not on the worksheet. Assign items 1 through 6 and item 11. Most of these answers land on friendly decimals, and item 6 needs the rates from items 3 and 4.
Extension
Ask these students to invent a sixth gauge whose depth and time are both fractions and whose rate matches Gauge 1 exactly, then to show the division that proves it. Have them explain why many different pairs of numbers give the same rate.
ELL supports
Pre-teach "gauge," "caught," "rate," and "per hour" with a picture of a marked cylinder beside a clock face divided into quarters. Provide the frame "Gauge ___ caught ___ inch in ___ hour, so its rate is ___ inches per hour" for items 1 and 2.