(1)5/8÷5+1/5×1/8
=5/8×1/5+1/5×1/8
=1/5×(5/8+1/8)
=1/5×6/8
=1/5×3/4
=3/20.
(2)(2/7+5/14)÷1/7
=(2/7+5/14)×7
=2+5/2
=4又1/2.
(3)8/13×1/9÷4/39
=8/13×1/9×39/4
=2/3.
(4)6分之1×3分支÷(5分之4-15分之7)(3分之几?)
(5)4-(1/4+3/8)÷1/4
=4-(1/4+3/8)×4
=4-(1+3/2)
=4-1-3/2
=3-3/2
=1又1/2.
(1)设全长为x,
列方程:(3/7)x=420
x=980
(2)设水蹈有x吨,
列方程:60÷(1-1/8)=x,
x=480/7.