SOLUTION: I have 20 surveys and my average is 84% how many 100% (perfect surveys) do i need to get my average above 91%

Question 972438: I have 20 surveys and my average is 84% how many 100% (perfect surveys) do i need to get my average above 91%
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
average = total/number.
Average is 0.84, number is 20, so total is 16.8
Let x = number of perfect surveys needed.
{16.8 +x}/(20+x) = 0.91
multiply by (20+x) both sides
16.8 +x = 18.2 +0.91 x
-1.4 =-0.09 x
need between 15 and 16 surveys, so round up to 16 surveys.
Check
36 will be the number of surveys.
The total will be 16.8+12=32.8
32.8/36=0.9111 (repeat)
Try 35 surveys (15 more)
31.8/35 =0.9086.
You need 16 more surveys.
RELATED QUESTIONS
My teachers grading scale is a little different.. 120% instead of 100%, I'll explain:... (answered by KMST)

if i have an average of 84% and my final exam is worth 20% of my final mark, what mark... (answered by ankor@dixie-net.com)

If I have an average of a 72 and I will take a test that's worth 20%. What grade do I... (answered by richwmiller)

If I have an average of 73% and my exam is worth 60% of my average how much do I need to... (answered by solver91311)

I have a 84 average and I get two 100 on major test grades what will my average... (answered by solver91311)

If my class average is 83.6 what do I need on my final (that's worth 20%) to get a B?... (answered by richwmiller,jerryguo41)

If i have an average of 78% and I need an average of 80% how many marks out of 60 do i... (answered by ewatrrr)

My average in my criminology class is 68%. what do i need on my final test which is 20%... (answered by ankor@dixie-net.com)

If I have a 97 average on my test which is 75% of my grade. The final is worth 25%, What... (answered by TimothyLamb)