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### Course: Pre-algebra>Unit 6

Lesson 2: Substitution & evaluating expressions

# Evaluating an expression with one variable

In this math lesson, we explore the expression 5 t plus 3 to calculate the cost of participating in a hospital raffle fundraiser. By evaluating the expression for different values of t, the number of tickets purchased, we find the costs for buying 1, 8, and 10 tickets, which are 8, 43, and 53 dollars, respectively. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• how do i solve if 8 is 90% of n
• Change 90% into a decimal: 0.90 or 0.9
Translate the key words: "of" = multiply and "is" means "="
Translate the phrase: "8 is 90% of n" becomes 8 = 0.90n
Solve for "n" by dividing both sides by 0.9

Alternatively, set up a proportion:
8/n = 90/100
Cross multiply and divide to solve for "n"

Hope this helps.
• hey guys i just started algebra any tricks becaus this is hard
• Yeah, i think that you should try learning simplfying and one step equations first. They are easy because it is what you know just in a basic form. work from there and you will get a basic understanding of algerbra and be able to work forward and go to harder stuff.
• Why is X the most used variable is it because of the x and y axis or some other reason
• yes, it is! x and y are commonly used as variables on khan, but what they are most famous for is the the x and y axis, but as sal says "You can use any variable but were going to use x and y" they just use it on khan for equations and other math problems often! btw off topic, im a fellow programmer two! nice to meet you!:D
• What happens if t is a decimal, a logarithmic function or even worse an exponential function?
• If "t" is a decimal, you do the same thing you would with a whole number.
• I love math!... (It's opposite day)
• If t=11, what is the answer?
• expression: 5t+3

If t=11:

(5x11)+3
=55+3
=58

Hope this helps!
• You got this guys! Even if it's hard, i believe in you!

Keep going!
• At , is 5. (1) not the same as 5 x x 1 ?
• If another operation is before the parentheses, then you don't multiply. If you have something like 3- (-3), you just subtract the -3.
If yo have 4*(5), you only multiply once.