How much pure acid should be mixed with 7 gallons of a 40 % acid solution in order to get an 80 % acid solution?

Given tan∅=4/3 and π< ∅< (3π)/2; find cos2∅ a. -24/25 b. 24/25 c. -24/7 d. -7/25

Twelve different video games showing substance use were observed and the duration times of game play (in seconds) are listed below. the design of the study justifies the assumption that the sample can be treated as a simple random sample. use the data to construct a 99% confidence interval estimate of μ, the mean duration of game play. 4028 4316 4816 4650 4036 5010 4833 4331 4307

M∠abc=138° and m∠def=31° . which statement is true about ∠abc and ∠def ? a: the angles are neither complementary nor supplementary. b: the angles are complementary. c: the angles are supplementary.