16.9乘以(2.5加7.5)
=16.9×10
=169不对。继续不带括号？16.9乘以2.5加7.5=16.9×.5+2.5×3=2.5×(16.9+3)=25×(20-0.01)=25×20-25×0.01=500-0.25=499.75得数不对写错了。不好意思16.9乘以2.5加7.5=16.9×.5+2.5×3=2.5×(16.9+3)=2.5×(20-0.1)=2.5×20-2.5×0.1=50-0.25=49.75