[(7又1/13+2.4除6又2/5)+2又5/8]乘5
=[(92/13+2.4除32/5）+21/8]乘5
=[(92/13+12/5除32/5）+21/8]乘5
=[(92/13+12/32）+21/8]乘5
=(92/13+96/32）乘5
=131/13乘5
=50又5/13