Declining Whales: Multiplying a Whole Number by a Percent
Grade Levels: 5 - 8
Overview
Students use their skill of multiplying a whole number by a percent to assess the population of certain species of whale.
Objectives
- Students will recall how to multiply a whole number by a percent.
- Students will understand that the population of many species of whales continues to decline.
- Students will read a graph to determine the current population of certain species of whales.
- Students will multiply a whole number by a percent to find the anticipated population of certain species of whales.
Materials
Procedure
- Introduce key vocabulary: endangered, extinct, species.
- Inform students that the number of fish in a particular imaginary lake has declined by 28 percent this year. There were 12,700 fish in the lake last year. How would one calculate how many fish are currently living in the lake? Elicit the response that the original population (12,700) must be multiplied by 28 percent in order to begin to find the solution. Tell students to multiply 12,700 by the decimal equivalent of 28 percent (.28).
- The product of this multiplication problem is the number of fish that have died this year. How many fish are left in the lake? Lead students to the reasoning that the solution (3,556) must be subtracted from the original number of fish (12,700) to find the number of fish in the lake right now.
- What if another 28 percent of these fish perish? Have students figure out how many fish will die and how many will be left. Remind them to start with the result figure 9,144 (not 12,700.)
- Go to http://archive.greenpeace.org/oceans/whaling/whalepopulations.html. Refer them to the species of whales and the original population levels. Inform them that although these species were protected in the year noted, in most cases their populations have still declined. Discuss some of the reasons for this (e.g., countries and fishermen are not honoring the protection; there is continued demand for whale-related products; there are environmental effects on the whales' habitat).
- Look at the "Latest Level" column. No one can accurately predict how much the population of each whale species will decrease in coming years; however, they can make some calculations and compare the results. Divide the class into five groups and assign each group two whale species: Blue and Bowhead, Bryde's and Fin, Gray and Humpback, Minke and Right, Sei and Sperm. By multiplying for their species, students can calculate the population decline over the course of three years, assuming a 12 percent decline each year. They should round decimals in order to arrive at whole numbers, rounding up if a decimal is 0.5 or greater, and down if it is less than 0.5.
Assessment
Extensions
- Discover TeacherVision's cross-curricular lessons and activities on Oceans and Animals.
- Research each of the whale species, including threats to their populations.
- Direct students to figure out the whale species populations for two more years, assuming that in Year 4 the population declined by 4 percent, and in Year 5 it declined by 3 percent.
