Question

Each second after shut-off, the speed of the blade is 2/3 of the speed in the previous second. After the first 8 s, the saw has turned 258 times. What was the speed of the saw before the motor shut off, to the nearest tenth of a turn per second?

I get 805.4 but I don't think I'm right.

Answer 1

i wanna answer this inequality of this graph f(x)= x -3 if x >= 3

Answer 2

You want the sum of the first 8 terms:

S8 = a(1-r^8)/(1-r) = a(1-(2/3)^8)/(1/3) = 2.883a

So, a = 258/2.883 = 89.49

Your answer is totally unreal. It would have turned 805.4 times in the 1st second, which is way more than the total turns after 8 seconds. I hope that is why you doubted it, and not just a vague uneasiness.

Answer 3

Thanks Steve, turns out my calculator is a bit sensitive..