The length of a spring under 30n tension is 20cm. When the length under 20n pressure is 15cm, what is the original length and progress coefficient of the spring To be specific,

Let the original length be x and the stiffness coefficient be K
be
（20-x）k=30
（x-15）k=20
Solution
x=17cm
k=10N/cm
PS: the one upstairs did something wrong,
The second is pressure,
So the force difference should be 20 + 30 = 50N

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