Population Problems

Video solutions to help Grade 7 students write and use algebraic expressions and equations to solve percent word problems related to populations of people and compilations.

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Common Core For Grade 7

New York State Common Core Math Grade 7, Module 4, Lesson 16

Lesson 16 Student Outcomes

• Students write and use algebraic expressions and equations to solve percent word problems related to populations of people and compilations.

Lesson 16 Classwork

Example 1 A school has 60% girls and 40% boys. If 20% of the girls wear glasses and 40% of the boys wear glasses, what percent of all students wears glasses?

Exercises 1–2
1. How does the percent of students who wear glasses change if the percent of girls and boys remains the same (that is, 60% girls and 40% boys) but of the 20% boys wear glasses and 40% of the girls wear glasses?
2. How would the percent of students who wear glasses change if the percent of girls is 40% of the school and the percent of boys is 60% of the school, and 40% of the girls wear glasses and 20% of the boys wear glasses? Why?

Example 2
The weight of the first of three containers is 12% more than the second, and the third container is 20% lighter than the second. The first container is heavier than the third container by what percent?

Exercise 3
3. Matthew’s pet dog is 7% heavier than Harrison’s pet dog, and Janice’s pet dog is 20% lighter than Harrison’s. By what percent is Matthew’s dog heavier than Janice’s?

Example 3
In one year’s time, 20% of Ms. McElroy’s investments increased by 5%, 30% of her investments decreased by 5%, and 30% of investments increased by 5%. By what percent did the total of her investments increase?

Exercise 4
4. A concert had 6,000 audience members in attendance on the first night and the same on the second night. On the first night the concert exceeded expected attendance by 20% while the second night was below the expected attendance by 20%. What was the difference in percent of concert attendees and expected attendees for both nights combined?