六年級數學題及答案：分數的四則混和運算
求1/3+1/15 +1/35+ 1/63 +1/99 +1/143
簡便方法：
1/3=1×(1/3)=1/2(1-1/3)
1/15 =(1/3)×(1/5)=1/2(1/3-1/5)
1/35=（1/5)×(1/7)=1/2(1/5-1/7)
1/63 =(1/7)×(1/9)=1/2(1/7-1/9)
1/99 =(1/9)×(1/11)=1/2(1/9-1/11)
1/143=(1/11)×(1/13)=1/2(1/11-1/13)
所以1/3+1/15 +1/35+ 1/63 +1/99 +1/143
=1/2(1-1/3)+1/2(1/3-1/5)+1/2(1/5-1/7)+1/2(1/7-1/9)+1/2(1/9-1/11)+1/2(1/11-1/13)
提公因式1/2得1/2(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13)
可觀察到式子中間部分都抵消，最后只剩下1/2(1-1/13)=6/13
也就是1/3+1/15 +1/35+ 1/63 +1/99 +1/143=6/13。
