1. Tính nhanh :
a, 1 + 7 + 13 + … + 427
b, 17 + 25 + 33 + … x 737
c, 97 . 37 + 54 . 67 – 13 . 37 + 67 . 46 + 16 . 37
1. Tính nhanh : a, 1 + 7 + 13 + … + 427 b, 17 + 25 + 33 + … x 737 c, 97 . 37 + 54 . 67 – 13 . 37 + 67 . 46 + 16 . 37
By Caroline
`a. 1 + 7 + 13 + …. + 427`
` = [(427-1):6+1]. (427+1)/2`
`=15408`
`b, 17+25+33+……+737`
`=[(737-17):8+1].(737+1)/2`
`= 33579`
`c,97.37+54.67-13.37+67.46+16.37`
`=37.(97-13+16)+67.(54+46)`
`=37.100+67.100`
`=100(37+67)`
`=100 . 104 = 10400`