GMAT tests your logical skills as well as your knowledge of math concepts. To score high, you need to remember various formulas, theorems. Also you need to master critical problem-solving skills.
Today I am going to take you through one problem -solving skill –
Attention to detail
Take this problem .
I am going to show you, two ways to solve this sum
Method 1 : The traditional approach
You need to choose the numbers which negate each other
For example Row 6 column 6 = 36.
Row 5 column 6 = -30 and Row 1 column 6 is -6
So 36+ (-30-6) =0.
You need to choose the right numbers
I have highlighted the different combinations with letters
|
1J |
-2I |
3H |
-4J |
5D |
-6A |
|
-2 |
4G |
-6C |
8G |
-10I |
12I |
|
3J |
-6B |
9H |
-12H |
15E |
-18B |
|
-4F |
8G |
-12F |
16F |
-20E |
24B |
|
5E |
-10 |
15 |
-20G |
25D |
-30D |
|
-6 |
12 |
-18C |
24C |
-30A |
36A |
Numbers left = 12 15 -6 -10 -2
Sum = 9
This method takes a long time
Method 2: Pattern recognition
This approach is a lot faster.
If you look at the numbers column-wise can you see a pattern(ignore
signs)
column 1: 1 2,3,4,5,6
column 2: 2x1,2x2,2x3,2x4,2x5,2x6
.
.
column 6: 6x1,6x2,6x3………..6x6
When the signs are inserted, then a pattern emerges i.e. = 1-2+3-4+5-6
lets calculate the sum of the repeating pattern 1-2+3-4+5-6 = -3
Hence column 1 adds upto -3
Next column will be -2+4-6+8-10+12 = -2 x(1-2+3-4+5-6)= -2x-3
= 6
Next column will be 3 x(1-2+3-4+5-6)= 3 x-3 = -9
Next column will be -4 x(1-2+3-4+5-6)= -4 x-3 = 12
Next column will be 5 x(1-2+3-4+5-6)= 5 x-3 = -15
Next column will be -6 x(1-2+3-4+5-6)= -6 x-3 = +18
Answer = -3+6-9 +12-15+18 = 9
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