Tex, an 85.0 kilogram rodeo bull rider is thrown from the bull after a short ride. the 520. kilogram bull chases after tex at 13.0 m/s. while running away at 3.00 m/s, tex jumps onto the back of the bull to avoid being trampled. how fast does the bull run with tex aboard?

The question above can be answered through using the concept of Conservation of Momentum which may be expressed as,
                 m1v1 + m2v2 = mTvT
where m1 and v1 are mass and initial velocity of Tex, 2s are that of the bull, and the Ts are the total. Then substituting,
                    (85 kg)(3 m/s) + (520 kg)(13 m/s) = (520 + 85)(vT)
The value of vT obtained from above equation is 11.6 m/s