Problem Solving

1 2 3 4 5 6 7
-2 -4 -6 -8 -10 12 14
3 6 9 12 15 18 21
-4 -8 -12 -16 -20 -24 -28
5 10 15 20 25 30 35
-6 -12 -18 -24 -30 -36 -42
7 14 21 28 35 42 49


I came across this question on the prep1 exam and looking for a shorter / faster way to do this? The question asks for the sum of all the numbers in the table.
Thanks

Here is the question typed out in a word document?

If you add up the first column you will find the sum is 4 and do the same for the second column.
You will find a symmetry

4 8 12 16 20 24 28 and add all these numbers.

But I don't think this is the best way to do it.
Should be a better way.

So the answer should be 112

I am sure somebody can come with a better explaination

Sum up the middle column and multiply by 7 for the number of rows, since each value in the middle column is the average for that row.

Here's another way:

Step 1: Simplify each row by taking out the lowest common factor - which is the leftmost column for each row. You'll find that each row will have the following after you simplify: (1+2+3+4+5+6+7) = 28.

Step 2: Add up the total of the lowest common factor for each row: (1-2+3-4+5-6+7) = 4

Step 3: Multiply results from Step 1 & Step 2: 28*4 = 112