# Grid problem

• May 9th 2011, 09:15 AM
IBstudent
Grid problem
Hi all,
I have a small question that I wish you can help me solve.
I have circled the questions that I cannot answer...(The question is attached)

Please show me the method of how to get the answer, which should be:
d (ii) g= x+2n and i= x+2+2n
d (iii) 4n

Thanks
• May 9th 2011, 12:09 PM
Auri
I might have no idea what I'm saying but here goes. n = 5. Since the 3 X 3 grid is chosen from the 5 x 5 grid or 3 x 3 grid is chosen from the n x n grid. If g = 11, and x = 1, then x+2n or 1+2(5) = 11. And if i = 13. Then x+2+2n or 1+2+2(5) = 13. Since cg-xi = 20, and n = 5, then 4n or 4(5) equals 20.

I hope that helped?
• May 9th 2011, 12:13 PM
SpringFan25
start from the point "x" in an nxn grid.

going "down one" will increase the number by n
going "right one" will increase the number by 1

Can you use this information to solve the problem?

Edit:not quite sure why i posted that since previous poster seems to have solved the problem :P
• May 9th 2011, 12:59 PM
Auri
Quote:

Originally Posted by SpringFan25
start from the point "x" in an nxn grid.

going "down one" will increase the number by n
going "right one" will increase the number by 1

Can you use this information to solve the problem?

Edit:not quite sure why i posted that since previous poster seems to have solved the problem :P

Your answer seems to make more sense x+2n or x, and 2 down.
• May 9th 2011, 07:17 PM
IBstudent
Thanks you!
I appreciate both your help :D
• May 9th 2011, 07:28 PM
IBstudent
Quote:

Originally Posted by SpringFan25
start from the point "x" in an nxn grid.
going "down one" will increase the number by n
going "right one" will increase the number by 1

I have a small doubt....
so now this formula (x+2n) can give me g in any grid, lets substitute this formula for a 3x3 grid. where n=3
1+3(3)=7, but it should be 11, why doesn't this formula work this way, it only works for the 5x5.

thanks
• May 10th 2011, 03:16 AM
SpringFan25
The 3x3 grid contains numbers from 1 to 9, so g cant possibly be 11.

in fact, there is only 1 way to take the 3x3 square from a 3x3 grid, which is this:

$\begin{array}{lll}1 & 2 & 3\\4&5&6\\7&8&9\\\end{array}$

g is 7 as predicted by the formula.
• May 10th 2011, 03:39 AM
IBstudent
Quote:

Originally Posted by SpringFan25
The 3x3 grid contains numbers from 1 to 9, so g cant possibly be 11.

in fact, there is only 1 way to take the 3x3 square from a 3x3 grid, which is this:

$\begin{array}{lll}1 & 2 & 3\\4&5&6\\7&8&9\\\end{array}$

g is 7 as predicted by the formula.

ow, now I get it.
i don't know what I was thinking..... stupid me!
I really appreciate your help :D