Calculating Final Speed of a Thrown Object with Changing Momentum

[quantumpanda]

A 60kg person is holding two 10kg blocks and she throws them one at a time at 5m/s.
What is her final speed?

What I get is,
after she throws the first rock 0=70v-50 so her speed is 5/7 m/s,
and after she throws the second 5/7 *70=60v-50 so her final speed is 5/3 m/s (1.67 m/s)

But the answer says 1.55 m/s which is less than the speed she would gain if she throws the two rocks simultaneously (5/3 m/s).
What am I doing wrong?

 

[Doc Al]

The speed of each thrown block is 5 m/s with respect to the person. As the person's speed changes, so does the speed of a thrown block with respect to the ground.

 

[quantumpanda]

The speed of each thrown block is 5 m/s with respect to the person. As the person's speed changes, so does the speed of a thrown block with respect to the ground.

Ofcourse... thank you!