Question

奥数题及答案：5/6-2/15+13/28-9/20=？

Answer 1

5/6-2/15+13/28-9/20= 5/6-2/15-9/20 +13/28=（50-8-27）/60+13/28=1/4+13/28=20/28=5/7
说明：先找容易通分的，试试计算后能不能再约分。

Answer 2

原式=(2+3)/(2*3)-(5-3)/(3*5)+11/28+2/28-(4+5)/(4*5)
=(1/2+1/3)-(1/3-1/5)+(4+7)/(4*7)+1/14-(1/4+1/5)
=1/2-1/3-1/3+1/5+1/4+1/7-1/4-1/5+1/14
=1/2+1/7+1/14
=(7+2+1)/14
=5/7

Answer 3

5/6-2/15+13/28-9/20
=5/6+13/28-(2/15+9/20)
=70/84+39/84-(8/60+27/60)
=109/84-49/84
=60/84
=5/7

Answer 4

原式=25/30-4/30+1/2-1/28-(1/2-1/20)=7/10+1/20-1/28=3/4-1/28=5/7

Answer 5

5/6-2/15+13/28-9/20=50/60-8/60-27/60+13/28=15/60+13/28=1/4+13/28=7/28+13/28=5/7