Math Question, your smarts are required

Hello Dopers!

My colleague and I came up with two completely different answers for the following question, which I’m sure will be a no brainer for y’all.

My computer program has been significantly rewritten, with speed improvement–

When I ran the pre-improvement test, the speed to process a given request was 170.37 seconds :smack:

After rewriting the program, the speed was .662 seconds. :smiley:

How much faster, percentage-wise, was the speed of the request?

Let me know if additional info is needed.

Thanks!!

Looks like about 25728% (that is, 170.32 / .662 * 100%).

Well, that’s different than what either of us got…

Since you’re asking for faster, your going to need to subtract. The difference then gets divided by the “old” number for reference to the “before” quantity.

In words: ((new - old) / old) * 100%)

Minor quibble: the second version is 25728% of the speed of the first version, making it 25628% faster than the first version.

Zeldar–so what’s your end result? Your calculation gives me -99.61143%. Does that translate to "We decreased the speed 99.61143%.)?

Sorry, I mean “We decreased the time it takes by 99.61143%.” OR “We increased the speed by 99.61143%”.

You decreased the time it takes by 99.61%, you increased the speed by 25636%. (Taran’s original calculation was a little off). The final result took 0.39% of the original time, and was 25736% of the speed of the first program.

Maybe if you take a less drastic change of times (not speeds) from something like 11 seconds to 4 seconds, the numbers won’t be as scary.

Your “percentage change” involves a difference expressed as a percentage of the original value.

And your statement of reducing the time is how I’d say it. Dealing with negative time seems a bit odd, but if you wanted to express it in terms of money and went from $11 to $4 it might aid the understanding of the idea.

To be more formal about it, speed is distance over time. In this instance, “distance” isn’t really relevant, but let’s call it “d” for now.

So, by Zeldar’s equation, we get:

(d/.662 sec - d/170.37 sec)/(d/170.37 sec) [sup].[/sup] 100%

The d’s and seconds divide out, giving us:

17037% [sup].[/sup] (1/.662 - 1/170.37)

which, when you multiply out, give you 25636%.

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