7.8×99=7.8×(100-1)=7.8×100-7.8×1=780-7.8=780-(10-2.2)=780-10+2.2=770+2.2=772.2
7.8x99=7.8x(100-1)=7.8x100-7.8=780-7.8=772.2
7.8×99=7.8×(100-1)=7.8×100-7.8×1=780-7.8=772.2
7.8*100-7.8+0.78=780-7.8+0.78=772.2+0.78=7720.98