How can you determine weather a fraction was equivalent to 2/5

Determine the mean and variance of the random variable with the following probability mass function. f(x)=( 729divided by 91) (1 divided by 9) superscript x baseline comma x equals 1,2,3 round your answers to three decimal places (e.g. 98.765).

X+y=-4 x-y=2 use elimination with adding and subtraction

There were 25 students who answered to a survey about sports. four-fifths of them like football. how many students like football?