a:b=5:3,求5a:2b及(2a+3b)/(a-b)
a:b=5:3,
设a=5t,则b=3t
5a:2b=(5*5t):(2*3t)=25t:6t=25/6
(2a+3b)/(a-b)
=(2*5t+3*3t)/(5t-3t)
=(10t+9t)/2t
=19t/2t
=9.5