Waves multiple choice quesion Watch

JakeRStudent
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A progressive wave in a stretched string has a speed of 20m/s and a frequency of 100Hz. What is the phase difference of two points 25mm apart?
A zero
B PI/4
C PI/2
D PI

I originally worked out the wavelength by use of the wave equation, and got 0.2m.
I then converted the 25mm to m which is 0.025m. By dividing 0.2 by 0.025 I got 8. Meaning that the two points are 1/8 of a wavelength apart. I then changed this into radians by use of a diagram.
I was just wondering if there was any better way to do the last section after figuring out the wavelength as the way I've done it has confused myself
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tamanna___
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From speed and frequency you can calculate wavelength which comes out to be 0.2 meters or 200 mm As 200 mm gives a phase difference of 360 or 2pi rads then 25 mm will give pi/4 rads

I found this as a solution online.. I dont know if it makes sense or not i havnt learnt about phase difference
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GarlicBread01
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If you know that the two points are 1/8 wavelength apart,
one whole wavelength = 2π so then

phase = 1/8 x 2π
= 1/4 π

atleast thats how I'd do it, not sure if theres an easier way
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