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## Introduction to inequalities with variables

Current time:0:00Total duration:2:54

## Video transcript

- The speed of sound is
approximately 768 miles per hour. When an object travels faster
than the speed of sound, it creates a sonic boom. And there's actually a whole video on how sonic booms are
created, on Khan Academy. I encourage you to watch it,
it is actually fascinating. But anyway, back to this question. Write an inequality to
represent, s, the speeds at which a moving object
creates a sonic boom. So we'll start an inequality, we'll do what they told us to. S, let's see. S has to be, they say when an object travels faster than the speed of sound. So our speed has to be greater
than the speed of sound. Our speed has to be greater
than the speed of sound, which is 768 miles per hour, so s has to be set greater than 768. Now another way we could have written that is that 768 needs to be less than s. We could have written 768
needs to be less than s. That's another way we could write it. In either case, our speed is going to be greater than 768 miles per hour. We check our answer. Let's do a few more of these. To cook a steak to medium-rare, it needs to have an internal temperature of 135 degrees Fahrenheit. A lower internal temperature
will undercook the steak. Write an inequality to represent all of the possible temperatures, t, of an undercooked steak. Well, to be an undercooked steak your temperature is going
to be less than 135 degrees. So your temperature, t,
is going to be less than. You could either just use the
less than on your keyboard, or you could click over here on less than. Your temperature is going
to be less than 135. We're assuming your temperature
is in Fahrenheit degrees. So your temperature needs to be less than Fahrenheit, less then 135 degrees, if you are going to have
an undercooked steak. So, you got that one right. Let's do a couple more.
Or one, let's do one more. Simone is going snowboarding tomorrow if the temperature is equal to or colder than five degrees celsius. Write an inequality to represent the temperatures at which
Simone will go snowboarding. So you might want to say "Oh, well "maybe you know that t is
less than five degrees." Remember, they're telling us that the temperature is equal to or colder, so she's even willing to go snowboarding if it's less than or
equal to five degrees. So instead of just saying less than, let's say less than or, whoops. Let's say less than or
equal to five degrees. So this inequality represented here, this shows us all of the temperatures at which she is willing
to go snowboarding. We check our answer and we got it right.