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In the queue for pretzels my grandfather is the 5 person starting from the front of the row and the 7 person from the end. How many people are waiting in the queue?
Method 1. If we count from the front of the row there are 4 people ahead of grandfather, if we count from the end there are 6 people besides him. To the sum of these two numbers we have to add the grandfather.
The result is 4 + 6 + 1 = 11.
Method 2. We sum the number of people from the front of the row and from the end and we subtract grandfather once, for he has been added twice.
The result is 5 + 7 - 1 = 11.
By learning math, you learn to think.