A bag contains 5 red balls, x blue balls. If the probability of choosing a black ball at random is 9/20.find the value of x

Rachel is studying the population of a particular bird species in a national park. she observes every 10th bird of that species that she can find in the park. her conclusion is that the birds living in the park who belong to that species generally feed on insects. rachel's sample is . based on the sample she picked, rachel's generalization is