Flightplan/ descent.

So flying the flying the qw 787

reaching TOD. Starting my descent an noticed in my fmc  that my speeds were different at different waypoints during flight.

using LNAV/VNAV

for eg.

Descending to 28000 from 37000 speed was 290 

then at lower altitude next waypoint 24000 was 270kts

then at a lower altitude/next waypoint.

speed was back up at 290kts And back down to 270kts and so forth until about 14000ft 

Sorry if it’s a dumb question.

i tried asking on the qw forums.

but says i am asking too many questions and spamming.

lol I tried to ask 2 questions. 

thanks

mike