use interval notation

Question

Ralph needs to earn a B in his Physics class. His current test scores are 91, 86, 78, and 71. his final exam is worth 6 test scores. in order to earn a B Ralph's average must be between 80 and 89 inclusive. what range of scores can Ralph receive on the final exam to earn a B in the course? use interval notation to express this range.

Answer 1

after taking the final exam it is as if Ralph took 10 tests altogether

Ralph's average must be between 80 and 89 inclusive to get a B average

800<91+86+78+71+6x<890 where x=final exam score

800<326+6x<890

800-326<6x<890-326

474<6x<564

474/6<x<564/6

79<x<94

Ralph can get a 79 up to a 94 on his final exam.