A sample of pure radioactive isotope is left to decay. After 40.0 days, the 1 point sample is placed in a mass spectrometer, and it is determined that only
25% of the original isotope remains. How long is the half-life?

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .

A. burning woodcombustion is the process of burning something. make brainliest if correct

Hcn is the correct answer leave a good rate and .

C. 6.94 is the correct answer y'all