5/7-5/9×5/7+4/9×2/7(简算)
问题描述:
5/7-5/9×5/7+4/9×2/7(简算)
答
5/7-5/9×5/7+4/9×2/7
=(1-5/9)×5/7+4/9×2/7
=4/9×5/7+4/9×2/7
=4/9×(5/7+2/7)
=4/9