计算:① -15―[―1-(4-20)]; ② (-3+)÷(-);③ 4×(-7)+(-2)2×5-4÷(-) ④(-)7×(-6)×(1)8―(―23)÷4×(-)
1.8×8.6+1.8×1.3+18%
100﹣98+96﹣94+92﹣90+…+76﹣74+72=
11+192+193+19994+199995=
=