Main content
Course: Grade 8 (TX TEKS) > Unit 3
Lesson 2: Representing problems with equations & inequalities- Writing equations to represent geometric problems
- Writing equations to represent problems
- Write equations to represent problems
- Writing inequalities to represent problems
- Writing inequalities to represent real-world problems
- Write inequalities to represent problems
© 2024 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Writing equations to represent problems
Explore writing equations to represent real-world problems involving coral samples. Created by Sal Khan.
Video transcript
- [Instructor] We're told A biologist is observing the heights
of two coral samples. Sample A is currently
eight centimeters tall and grows two centimeters
taller every year. Sample B is currently 15 centimeters tall and grows 1.5 centimeters
taller every year. The biologist wants to
know how long it will take for their heights to be the same. Let t represent the
number of years from now. Write an equation to
represent the situation. So like always pause this video, see if you can figure this out and then we can work on this together. Alright, now let's do it together. So this first statement, it says, sample A is currently
eight centimeters tall and grows two centimeters
taller every year. How can we write an
expression for sample A? Well, it's already eight centimeters tall. We'll just assume all the
numbers are in centimeters, and every year it grows two centimeters. And each year we'll represent
t to be the number of years. So the height of sample A is
going to be eight plus two times the number of
years that have gone by. Fair enough. Now let's
think about sample B. It's currently 15 centimeters tall and grows 1.5 centimeters
taller every year. So an expression for
the height of sample B after two years would be 15 centimeters plus 1.5 times the number
of years that have gone by. Fair enough. Now we want an equation
to represent the situation for how long will it take for their heights to be the same, for the heights to be the same. Well, this is their
heights after two years. So we just have to say, well we want these two things to be equal and then solve for t and that will tell us how
many years will it take for their heights to be
the same and we're done.