X+ 53 = 87 what does "x" mean. plz explain!

△def is similar to △stu. write a proportion that contains st and su.

How can you use equivalent fractions to know that 43/200 is between 1/5 and 1/4?

Nielsen media research wants to estimate the mean amount of time (in minutes) that full- time college students spend watching television each weekday. find the sample size necessary to estimate the mean with a 15-minute margin of error. assume that a 95% confidence level is desired. also assume that the population standard deviation is known to be 112.2 minutes.