Mean Particle Size & Variance?

An important factor in solid missile fuel is the particle size distribution. Significant
problems occur if the particle sizes are too large. From production data in the past, it has been determined that the particle size (in micrometers) distribution is characterized by:

š‘“(š‘„) = { 3š‘„ ^āˆ’4Ā  Ā  Ā  š‘„ > 1Ā 
Ā  Ā  Ā  Ā  Ā  Ā  0Ā  Ā  Ā  Ā  Ā  Ā  Ā  š‘’š‘™š‘ š‘’š‘¤ā„Žš‘’š‘Ÿš‘’

Find the mean particle size. Find the variance of X.Ā 

2017-04-11T00:37:33.809Z