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## Pre-algebra

### 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.

## Video transcript

A local hospital is holding a raffle as a fundraiser. The individual cost of participating in the raffle is given by the following expression-- 5t plus 3, or 5 times t plus 3, where t represents the number of tickets someone purchases. Evaluate the expression when t is equal to 1, t is equal to 8, and t is equal to 10. So let's first take the situation where t is equal to 1. Then this expression right over here becomes-- and I'll use that same color-- becomes 5 times 1. 5 times 1 plus 3. 5 times 1 plus 3, and we know from order of operations, you do the multiplication before you do the addition. So this will be 5 times 1 is 5 plus 3, and then this is clearly equal to 8. Now let's do it when t is equal to 8. So when t is equal to 8, this expression becomes-- and I'll do the same colors again-- 5 times 8 plus 3. Same color of green. And once again, 5 times 8 is 40, and then we have the plus 3, there so this is equal to 43. And so we have the last situation, with t is equal to 10. I'll do that in blue. So we have 5 times 10. So 5t is 5 times 10. Instead of a t, put a 10 there. 5 times 10 plus 3. That's a slightly different shade of green, but I think you get the idea. 5 times 10 is 50. We do 50, and then we're going to have to add 3 to that, and that is equal to 53. And we're done.