How many neutrons are present in atoms of argon-39?

What is the frequency of a light wave with a wavelength of 620nm

Explain why the aperture of the spherical mirror should be small compared to the radius of curvature of the mirror.

The force acting on a beam was measured under the same operating conditions and a sample of 5 data points was collected. this process was repeated by 3 observers. the pooled standard deviations of these 3 data sets was 1.21. determine the true mean force using all pooled data (with a 95% probability). the result should look like this: true mean = mean +/- margin of error