Question: How many possible points is the quiz worth?
Answer: 25
Question: How many questions did you miss?
Answer: 1
Question: How many points was each missed question worth?
Answer: 2
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Explanation for the answers above:
There are 15 questions total. You answer 5 one-point questions and 9 two-point questions correctly. So you've answered 5+9 = 14 questions correctly out of the 15 total.
So you missed 1 question
The missed question point total is unknown for now. Call it x.
So far you've earned 5*1+9*2 = 5+18 = 23 points. Adding on the x points from what you missed and there are 23+x total points to earn (assuming you get 100%)
So this means
23/(23+x) = 0.92
because you earned a 92%
Solve for x
23/(23+x) = 0.92
23 = 0.92(23+x) ... multiply both sides by (23+x)
23 = 0.92*23+0.92*x ... distribute
23 = 21.16+0.92*x
23-21.16 = 21.16+0.92*x-21.16 ... subtract 21.16 from both sides
1.84 = 0.92*x
0.92*x = 1.84
0.92*x/0.92 = 1.84/0.92 ... divide both sides by 0.92 to isolate x
x = 2
The missed question was worth x = 2 points
There are 23+x = 23+2 = 25 points total. So you are close when you wrote 24