搵人幫我計兩條6年級數-.-20分

a. 51+53+55+......................+95+97+99 = ?
( 51 + 99 ) / 2 x 25 = 1875

b. 2+4+6+........................+96+98+100 = ?

( 2 + 100 ) / 2 x 50 = 2550

a. 51+53+55+......................+95+97+99 = ?
51+53+55+......................+95+97+99
=[(99-51)/2+1]*(99+51)/2
=(48/2+1)*150/2
=(24+1)*150/2
=25*150/2
=3750/2
=1875

b. 2+4+6+........................+96+98+100=?
2+4+6+........................+96+98+100
=[(100-2)/2+1]*(100+2)/2
=(98/2+1)*102/2
=(49+1)*102/2
=50*102/2
=5100/2
=2550

搵人幫我計兩條6年級數-.-20分
a. 51+53+55+......................+95+97+99 = ?
b. 2+4+6+........................+96+98+100 = ?

-_-thz'

the sum is (首項+未項)*項數/2
a. (51 +99)*25/2
=1875
b. (2 +100)*50/2
=2550

a.51+53+55+......................+95+97+99 = 1875
b.2+4+6+........................+96+98+100 = 2550

a. =(51+99)x 25/2 = 1875

b. = (2+100)x50/2 = 2550