Jetstreams are streams of high-moving west-to-east winds (200mph to 300mph, source) which most pilots are trained to use to cut down on their fuel costs (source). In the same linked article, it mentions private jets almost always fly at maximum speed anyway, even when on a jetstream.
Assuming a pilot maintains the same airspeed before and after entering a jetstream, how much would be the expected change in groundspeed in practice? Is it just the airspeed plus the tailwind?
I imagine it depends on the type of the aircraft, so consider only a typical commercial airplane (Boeing, Airbus? I'm not sure which one is more typical).
I'm just curious in knowing how the plane's speed is affected and why it changes that way.