Worksheet Grade 7 Math

Cobalt Springs Dam Reservoir: A Grade 7 Percent-Change Worksheet

A grade 7 worksheet using a fictional dam's reservoir storage to practice percent of capacity, percent increase, and percent decrease across a season.

Grade: Grade 7
Subject: Math
Material: Worksheet
Time: 35 min
Prep: No prep
Materials: Calculator

Standards

7.RP.A.3 Common Core Math

Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

How this material aligns: Items 1 through 9 ask students to find percent of capacity, percent increase, and percent decrease on reservoir storage, the multistep percent work this standard targets.

All materials for 7.RP.A.3 →

7.EE.B.3 Common Core Math

Solve multi-step real-life and mathematical problems posed with positive and negative rational numbers in any form (whole numbers, fractions, and decimals), using tools strategically, and assess the reasonableness of answers using mental computation and estimation strategies.

How this material aligns: Item 10 has students carry a starting amount through a percent rise and then a percent fall, a multistep rational-number problem whose answer they check for reasonableness.

All materials for 7.EE.B.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will find what percent of capacity a reservoir holds from its storage and full capacity.
Students will calculate percent increase and percent decrease for changing reservoir storage.

Vocabulary

Reservoir: A human-made lake, usually created by a dam, that stores water for later. Reservoirs supply cities and farms and help control floods.

Also: capacity, percent increase, percent decrease

Teacher overview

The fictional Cobalt Springs Dam holds back a reservoir that a town uses for water and boating. Its storage rises with spring runoff and falls through the summer as people use more water. This worksheet has students track that storage as percent of capacity, percent increase, and percent decrease. Watch for the common error of finding a percent change against the wrong number: a percent decrease is always taken from the larger, earlier amount, not the smaller one.

Cobalt Springs Dam Reservoir: A Grade 7 Percent-Change Worksheet — Grade 7 Math

Name: ____________________________ Date: ______________

Student Worksheet

The reservoir behind Cobalt Springs Dam has a full capacity of 40,000 acre-feet. Use that capacity for every item below.

Right now the reservoir holds 30,000 acre-feet. What percent of capacity is that?
Spring runoff raises storage from 30,000 to 38,000 acre-feet. What is the percent increase? Round to the nearest tenth.
What percent of capacity is 38,000 acre-feet?
In summer, water use drops storage from 38,000 to 30,400 acre-feet. What is the percent decrease?
The dam keeper wants the reservoir at least 60 percent full for boating. How many acre-feet is 60 percent of capacity?
Storage falls to 24,000 acre-feet. By what percent is that below the full capacity of 40,000 acre-feet?
The power plant runs best above 70 percent of capacity. Storage is 26,000 acre-feet. Is that above or below the 70 percent mark, and by how many acre-feet?
A wet year raises storage 15 percent from 30,000 acre-feet. What is the new storage?
The town plans a 5 percent cut in water releases. Last year it released 12,000 acre-feet. How many acre-feet are planned after the cut?
Start at 30,000 acre-feet. The storage rises 10 percent, then later falls 10 percent. Show that the reservoir does not return to 30,000 acre-feet, and explain why.

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: 75 percent. 30,000 ÷ 40,000 = 0.75, which is 75 percent of capacity.
Answer: About 26.7 percent. The rise is 38,000 − 30,000 = 8,000 acre-feet. Percent increase = 8,000 ÷ 30,000 = 0.2667, or about 26.7 percent.
Answer: 95 percent. 38,000 ÷ 40,000 = 0.95, which is 95 percent.
Answer: 20 percent. The drop is 38,000 − 30,400 = 7,600 acre-feet. Percent decrease = 7,600 ÷ 38,000 = 0.20, or 20 percent.
Answer: 24,000 acre-feet. 60 percent of 40,000 is 0.60 × 40,000 = 24,000 acre-feet.
Answer: 40 percent below. The gap is 40,000 − 24,000 = 16,000 acre-feet. 16,000 ÷ 40,000 = 0.40, or 40 percent below full.
Answer: Below, by 2,000 acre-feet. 70 percent of 40,000 is 28,000 acre-feet; storage of 26,000 is 28,000 − 26,000 = 2,000 acre-feet below that mark.
Answer: 34,500 acre-feet. A 15 percent rise means multiplying by 1.15: 30,000 × 1.15 = 34,500 acre-feet.
Answer: 11,400 acre-feet. A 5 percent cut means multiplying by 0.95: 12,000 × 0.95 = 11,400 acre-feet.
Answer: 29,700 acre-feet, so it does not return to 30,000. The 10 percent rise gives 30,000 × 1.10 = 33,000 acre-feet. The 10 percent fall is taken from 33,000, not 30,000: 33,000 × 0.90 = 29,700 acre-feet. The fall is larger in acre-feet than the rise because it comes off a bigger amount, so the final storage is below the start.

Differentiation

Support

Give students the difference step already set up for the percent-change items, such as "38,000 − 30,000 = ___", so they can focus on dividing by the correct starting amount. Provide a printed reminder that percent increase and percent decrease both divide by the earlier amount.

Extension

Ask students to find one storage amount that is exactly 82.5 percent of capacity, then design a rise-and-fall pair of percents that would leave the reservoir higher than it started, and prove it with the numbers.

ELL supports

Pre-teach "capacity," "increase," and "decrease" with arrows pointing up and down beside a drawing of a reservoir. Provide sentence frames such as "The change is ___ acre-feet, and ___ ÷ ___ = ___ percent" for the percent-change items.