Tính nhanh : a, 2 + 4 + 6 + … + 100 b, 1 + 3 + 5 + … + 99 c, 37 . 63 + 29 . 47 + 63 . 63 + 53 . 69 d, 1 + 4 + 7 + 10 + … + 154

a, 2 + 4 + 6 + … + 100

=[(100+2)/2].[(100-2)/2+1]

=51.50

=2550

b,1 + 3 + 5 + … + 99

=[(99-1)/2+1].[(99+1/2]

=50.50

=2500

c,37 . 63 + 29 . 47 + 63 . 63 + 53 . 69

=63(63+27)+(1363+3657)

=6300+5020

=11020

d,1 + 4 + 7 + 10 + … + 154

=[(154-1)/3+1].(154+1)/2

=52.155:2

=4030