physics
posted by Jen .
an unstretched hanging spring is 50cm long. suspending a 100N weight from it makes its lenght 60cm. Adding another 100N weight will make the spring 
60cm, 70 cm, 80 cm, 100 cm, or 120 cm.
No idea how they came up with any of the five ??? My answer was different!
Please help!

The amount of stretching is proportional to the weight applied. That's called Hooke's law.
Since 100N stretches the spring 10 cm, 200 N will stretch it 20 cm. Add that to the original unstretched length.
50 + 20 = ___ cm