# Thread:

1. ## Town Hall Tiles

The diagram above (sorry my diagram isnt too great..) contains black and white tiles in a diamond formation. There are 7 tiles across and 25 tiles in total. Now I need to find how many tiles there would be in total, if the number of tiles across was 149. The formula I am using is n+x^2/y

So for the 7 across, the formula would be 7+x^2/y = 25

The only problem is, I cant work out what x and y are.

If you could help me finding what x and y are, that would be greatly appreciated.

Holly.

2. Originally Posted by everydaysahollyday

The diagram above (sorry my diagram isnt too great..) contains black and white tiles in a diamond formation. There are 7 tiles across and 25 tiles in total. Now I need to find how many tiles there would be in total, if the number of tiles across was 149. The formula I am using is n+x^2/y

So for the 7 across, the formula would be 7+x^2/y = 25

The only problem is, I cant work out what x and y are.

If you could help me finding what x and y are, that would be greatly appreciated.

Holly.
The standard formula for this would be $\dfrac{(n^2+1)}{2}$

In your case, working backwards, your x & y values will be:

$x = \dfrac{n-1}{2} \,\,$ --&-- $\,\, y = 0.5$

for n=149

$x = \dfrac{149-1}{2} = 74$ ; $149 + \dfrac{74^2}{0.5} \, = \, 149 + \dfrac{5476}{0.5} = 11101$

just to check

$\dfrac{(149^2+1)}{2} = 11101$

Hope that helps
.

3. In case this helps, Aidan's formula "comes from" the formula:
sum of 1st n odd numbers = n^2; like 1 + 3 + 5 = 3^2

In your example, this occurs twice (above and below the middle row),
hence 2(1 + 3 + 5) + 7 = 25
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