Answer:
The last quiz score must be at least an 80 to get the average to be a 70.
Step-by-step explanation:
In order to find this, you need to take the average of the 4 test scores along with the unknown test score (x). So, to find an average, we add all the numbers together and divide by the amount of tests taken. We can then set this equal to 70 since that is the minimum average.
(60 + 64 + 75 + 71 + x)/5 = 70 ------> Multiply both sides by 5
(60 + 64 + 75 + 71 + x) = 350 -----> Combine like terms
270 + x = 350 -----> Subtract 270 from both sides
x = 80
