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How do you sum more than two numbers quickly?
To sum more than two numbers quickly, follow these easy steps:
- Don't sum the numbers pairwise.
- Stack the numbers vertically, and align them to the right.
- Compute the sum of each column of digits, starting from the right.
- Proceed until you reach the last digit of the longest number.
That's it!
What is the result of the addition of 41,381 and 3,819?
45,200. To calculate the sum of 41,381 and 3,819:
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Stack the numbers aligned to the right.
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Sum the rightmost numbers: 9 + 1 = 10. Save 0 and lend 1 to the digits to the left.
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Sum 8 and 1 and add the 1 from the step before: 8 + 1 + 1 = 10. Save 0 and carry the one.
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Sum 3, 8, and the 1 from step 3.: 8 + 3 + 1 = 12. Save 2 and carry 1.
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Sum 1, 3, and the 1 from above: 1 + 3 + 1 = 5.
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Build the result: 45,200.
Why is plus the symbol for addition?
Historians speculate that the symbol + came to represent the addition as the result of a lengthy modification of the Latin conjunction et. The introduction of the symbol + for addition is relatively recent, dating back to the 14th century. Before that, different symbols were used, including pΜ and the bidirectional glyph used by Egyptians.
I don't think there is a way to get $30$ using the numbers from that list because all those numbers are odd. We know that odd + odd = even (that's the sum of any two numbers from the list) and even + odd = odd (we add one more number from the list to the sum which is even). So, the sum is always going to be odd, but $30$ is even!
It's actually impossible since all numbers are odd and $30$ is even.
Notice that every odd number can be represented as $2n+1$. Thus $$(2n+1)+(2k+1)+(2t+1)=2Β·(n+k+t+1)+1$$ which is odd and not even