<span>valid. She used a representative sample
</span>because she correctly found the average and 18,000 is a reasonable number to get for a the problem
780 (or c)
I think this is correct because 4 x 5 = 20 x 5 = 100 and 100 x 5 = 500
500 + 280 = ????
780
Answer: 288, 576, 1152
Step-by-step explanation: What you do here is that you multiply every number by two. You start by doing 18 times 2, which equals 36. Then you do 36 times 2, which equals 72. You keep on doing this until you get the answers needed.
Hope this helped!! :)