  There exist several approaches exploiting Lie symmetries in the reduction of
boundary-value problems for partial differential equations modelling real-world
phenomena to those problems for ordinary differential equations. Using an
example of generalized Burgers equations appearing in nonlinear acoustics we
show that that the "direct" procedure of solving boundary-value problems using
Lie symmetries firstly described by Bluman is more general and straightforward
than the method suggested by Moran and Gaggioli in [J. Eng. Math. 3 (1969),
151-162]. After the group classification of a class of generalized Burgers
equations with time-dependent viscosity is performed we solve an associated
boundary-value problem using the symmetries obtained.
