Question

Give the sum of the number from 11 to 20​

Answer 1

Answer:

The answer is 155, but here is a way to easily calculate it (at least easy for me).

Match up all the numbers from 11 to 19 in pairs, so that the sum of each pair equals 30. 11 with 19, 12 with 18, 13 with 17, and 14 with 16. Obviously , it doesn’t include the middle number, 15, and the last number, 20. However, now that you have 4 pairs that add up to 30 each and 15 and 20, you can easily add it. 30 times 4 is 120, + 15 + 20 = 155