SOLUTION: What term in the sequence (1.6,1.2,0.8,0.4,...) is -38.4 ? I guessed 99 but was marked wrong . I don't know how to do this , please help me :)

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equation Customizable Word Problems -> SOLUTION: What term in the sequence (1.6,1.2,0.8,0.4,...) is -38.4 ? I guessed 99 but was marked wrong . I don't know how to do this , please help me :)      Log On


   

Question 118654: What term in the sequence (1.6,1.2,0.8,0.4,...) is -38.4 ? I guessed 99 but was marked wrong . I don't know how to do this , please help me :)
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Look at the terms and see if you can determine the pattern.
First term = 1.6
Second term = 1.6-0.4 = 1.2
Third term = 1.6-0.4-0.4 = 0.8
Fourth term = 1.6-0.4-0.4-0.4 = 0.4
I think you can see the pattern.
Nth term = 1.6 - 0.4*(N-1)
Now that you have the formula, set it equal to the number to find N.
1.6-0.4%2A%28N-1%29=-38.4
-0.4%2A%28N-1%29=-40.0 Subtract 1.6 from both sides of the equation.
N-1=100Divide both sides by 0.4.
N=101
Check your answer with your original formula.
101st term = 1.6 - 0.4(101-1)=1.6-40.0=-38.4.
The answer checks out.