# Thread: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadsheet!

1. ## Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadsheet!

Firstly let me apologise for my lack of maths skills!! I work as a sports coach and I知 very adept at the day to day calculations I need but I知 building a spreadsheet and have hit a problem.

Basically I need to calculate how many times a number has to be doubled to match a larger number. For example 250 meters (0.25km) has to be doubled twice to match 1km. Ideally I need to calculate this with numbers that don稚 really fit.

For example 0.4km into 1km!!?? Or 1km into 5km??

Any help would be appreciated and sorry if this is super simple as so am!

Morgan

2. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

use logarithm base 2. A spreadsheet program has this functionality built in.

so, for example, from 0.25 to 1km , we would first divide

$\frac{\text{target}}{\text{initial}}=\frac{1}{0.25 }=4$

then $\log (4,2)=2$ therefore we must double twice to hit the target

another example, 1 to 5km, divide to get 5 and then $\log (5,2)=2.32$

therefore doubling twice is under target and doubling three times is over target

3. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

10 : 1000
10 + 20 + 40 + 80 + 160 + 320 + 640 = 1270

a = initial number (10)
t = target number (1000)
n = number of doublings (?)
Formula:
n = log(t/a + 1) / log(2) - 1
n = 5.658...

z'dat clear nuff Morgan?

4. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

Thanks folks!! I'll give this a whirl but no doubt I'll be back with another question!

5. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

Are you having problems using the spreadsheet or just the math?

-Dan

6. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

Just the maths, pretty ok with spreadsheets but any thoughts/advice would be appreciated

7. ## Re: Hi Everyone, I知 a sports coach who needs help with a calculation in a spreadshee

Why do you need to calculate this with numbers that don稚 really fit? There are going to be more times
numbers that don稚 really fit.

In your first example, 250 meters (0.25km) has to be doubled twice to match 1km so the answer you should get in your spreadsheet should be 2. In your second example. 0.4km into 1km the answer you should get is "more than once". What does the different types of answers mean to you when you see them in your spreadsheet?

Steve