Brain Teasers
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Divide the numbers from 1 to 20 into 10 pairs. Multiply the numbers in each pair, then add the ten products.
What is the difference between the maximum possible sum and the minimum possible sum?
What is the difference between the maximum possible sum and the minimum possible sum?
Hint
If you can't get it, try 1 to 4.1*2+3*4, 1*3+2*4, 1*4+2*3...
Answer
The maximum possible sum is 1*2+3*4+...+19*20=1430.The minimum possible sum is 1*20+2*19+...+10*11=770.
1430-770=660.
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