What is the value of y in the arithmetic sequence y + 6, 12, 3y?
Set it up with the interval in an equality. (12) – (y + 6) = (3y) – (12)
12 – y – 6 = 3y – 12
Let's put all the "Y"s on one side and
all the numbers on the other side 18 = 4y
Swap sides because I like the unknowns
to be on the left. No other reason. 4y = 18
Divide both sides by 4 y = 18/4
y = 4.5
Check answer: (y + 6) , 12 , 3y
(4.5 + 6) , 12 , (3 • 4.5)
10.5 , [add 1.5] 12 , [add 1.5] 13.5
looks good
