In order to afforest the North Slope Park, it is necessary to lay 5 1 meter long water pipes. 6 3m finished pipes, length12m. If it takes 5 minutes to splice an interface, it won't work.

5×(5 1÷3- 1),

=5× 16,

=80 (minutes);

(2) Mixed application of two kinds of pipelines:

5 1÷ 12=4 (root) ... 3 meters,

So we use 1 root length 3 meters and 4 root length 12 meters.

The splicing time is:

5×(4+ 1- 1),

=5×4,

=20 (minutes);

80 minutes > 20 minutes;

Therefore, the second scheme is the most time-saving;

Answer: It is the most time-saving to splice 1 piece with a length of 3m and 4 pieces with a length of12m.