How do you calculate 1+2+3+4+5+6+7+8+9+10 quickly?

The quickest method is found from a principle that adding a group of consecutive numbers you divide the numbers into pairs and start 1 + 10 = 11, there are 5 pairs of numbers adding up to 11( 2 +9, 3+8, 4 + 7, 5+6) therefore 5 x 11 = 55. Thank you for the question. by Graham C Lindsay