原式=(-13)×2/3-0.34×2/7+(-13)×1/3-5/7× 0.34
=[(-13)×2/3+(-13)×1/3]-(0.34×2/7+5/7 ×0.34)
=(-13)×(2/3+1/3)-0.34×(2/7+5/7)
=(-13)×1-0.34×1
=-13-0.34
=-13.34