7分之8*(5分之4-3分之2)/15分之4
=(8/7)×(12/15-10/15)/(4/15)
=(8/7)×(2/15)/(4/15)
=(8/7)×(1/2)
=4/7;
1.3/0.9+1.5/0.9+1.7/0.9
=(1.3+1.5+1.7)/0.9
=4.5/0.9
=5;