maths!!!!!!!!! p.6........

1. 2+4+6+.......+100
=2 x ( 1+2+3+....+50)
=2 x 50 x (50+1) / 2
=50 x 51
=2550

2. 1+3+5+......+99
=(1+2+3+.......+100) - 2-4-6-8-....-100
= 100 x (100+1) / 2 - 2550
=5050- 2550
=2500

3. 101 + 102 + ....... + 150
= 50 x 10 + ( 1+2+3+....+50)
= 500 + 50 x (50+1) / 2
= 500 + 1275
= 1575

1) 2+4+6+.............. +100
=2(1+2+3+...+50)
=2(50)(50+1)/2
=2550
_________________

2)1+3+5+............ .+97+99
=Sum of all 100 numbers-sum of all even number within 100
=(1+2+...+100)-(2+4+6+.............. +100)
=(100)(100+1)/2-2550<==sum of all even number was found
=2500
_______________
3)101+102+103+...... .......+150
=100*50+(1+2+3+...+50)<== 因為由101至150 有50個100
=5000+(50)(50+1)/2
=5000+1275
=6275
上面那位第三條的答案就錯乘為50*10,實為50*100才對

2006-11-08 18:41:32 補充：
有無攪錯,明明這個答案是錯的.你到底懂不懂看公式?