Erica wants to know how many books on average are in school libraries in her county. she randomly calls 50 school libraries in her county and finds out how many books they have. she adds the number of books together and divides by 50. her conclusion is there are an average of 18,000 books in a school library. erica's conclusion is
a) invalid. her sample size is too small.
b) invalid. her sample size is too large.
c) valid. she used a representative sample.
d) bias. she wants schools to buy more new books.

i need the table so i can see

step-by-step explanation:

x + y = 90 5x – 10y = 90 90 – 10y = 5x 90 + 10y = 5x

step-by-step explanation:

last month maria hiked the 5-mile mountain trail a number of times and she hiked the 10-mile canal trail several times. let x represent the number of times she hiked the 5-mile trail, and let y represent the number of times she hiked the 10-mile trail. if she hiked a total of 90 miles, which equation can be used to find the number of times maria hiked each trail? x + y = 90 5x – 10y = 90 90 – 10y = 5x 90 + 10y = 5x