Question

Music Lessons. Band members at Colchester Middle School are expected to average at least 20 min of practice time per day. One week Monroe practiced 15 min, 28 min, 30 min, 0 min, 15 min, and 25 min. How long must he practice on the seventh day if he is to meet expectations? A) 26 min. B) 27 min. C) 28 min. D) 30 min.​

Answer 1

For this you need to calculate the average, but with a variable for one of the numbers. To calculate average you add up all the terms and then divide by the number of terms, so you get the equation

(15 + 28 + 30 + 0 + 15 + 25 + x)/7 = 20

From there, you can multiply both sides by 7

15 + 28 + 30 + 0 + 15 + 25 + x = 140

Then combine like terms

113 + x = 140

And finally subtract 113 from each side.

x = 27

That gives us our answer for how many minutes he needs to practice on the final day to meet the average: 27 minutes or answer B.