Writing Equations

Turning Words into Equations  Similar to turning words into expressions  The word is tells you where your equal sign goes Write each sentence as an algebraic equation: A number increased by 9 is 15 n + 9 = 15 Twice a number is 18 2n = 18 Four less than a number is 20 n – 4 = 20 A number divided by 6 is 8 n/6 = 8

Twice a number, decreased by twenty-nine, is seven 2a – 29 = 7 Thirty-two is twice a number decreased by eight 32 = 2b - 8 Twelve is sixteen less than four times a number 12 = 4p - 16

Writing Equations for Word Problems Example: Bhavin’s age 7 years from now will be 20.  We don’t know Bhavin’s current age  We do know in 7 years she will be 20  We should pick a variable to represent the unknown value. In this case, it’s Bhavin’s age. Let’s let a represent Bhavin’s age So, the equation to figure out Bhavin’s age will be: a+7 = 20

We use equations to solve for the unknown or variable. This means, we want to figure out what the variable is. Bhavin’s age 7 years from now will be 20. So, how old is she now? Let a represent how old she is now a + 7 = 20 a + 7 – 7 = 20 – 7 a = 13 Solution: Bhavin’s current age is 13

How could we CHECK to see if our solution is right? Look back: Let a represent how old she is now a + 7 = 20 a + 7 – 7 = 20 – 7 a = 13 Solution: Bhavin’s current age is 13 Check: When a= 13, a +7 = 20 LSRS a = (13) + 7 = 20

Eleni is x years old. In thirteen years she will be twenty-four years old. x + 13 = 24 Each piece of candy costs 25 cents. The price of h pieces of candy is $ h = 2.00 Suzanne made a withdrawal of d dollars from her savings account. Her old balance was $350, and her new balance is $ – d = 280 A large pizza pie with 15 slices is shared among a group of p students so that each student’s share is 3 slices. 15/p = 3