1 m/h
(D) 0 5 m/h
Summary
® If a quantity y varies with another quantity x, satisfying some rule 
( )
y
=f x
,
then dy
dx  (or 
f( )
′x
) represents the rate of change of y with respect to x and
0
x x
dy
dx
=
   
 (or 
( )0
′f x
) represents the  rate of change of y with respect to x at
0
x
=x ® If two variables x and y are varying with respect to another variable t, i e