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Simple math

Anonymous Fri 15 May 16:07:58 2020 No.11675744 View Reply Original Report

Quoted By: >>11675915 >>11676041 >>11676139 >>11676238 >>11677985 >>11678027

Still a nice problem

Anonymous

Anonymous Fri 15 May 2020 16:56:18 No.11675915 Report

Quoted By: >>11676119

>>11675744
I will guess the number 8 because I like the number 8.

Anonymous

Anonymous Fri 15 May 2020 17:33:15 No.11676041 Report

Quoted By: >>11676119 >>11678131 >>11678731

>>11675744
s1/n = 80, s1 = 210 + x ;x is anon's current total score
s2/n = 85, s2 = 180 + x ;assuming anon cannot skip the third test, and, takes the zero such that n is equal for both situations.

s1 = 80n
s2 = 85n
s1/80 = s2/85
s1(85) = s2(80)
(210 + x)(85) = (180 + x)(80)
17850 + 85x = 14400 + 80x
x = -690

;(210 + x)/n = 80
(210-690)/n = 80
-480/n = 80
-480=80n
-6 = n
;(180 + x)/n = 85
(180 - 690)/n = 85
-510/n = 85
-510 = 85n
-6 = n

n-3 = ?
-6-3 = -9
Clearly anon has done negative nine tests.

Anonymous

Anonymous Fri 15 May 2020 18:00:31 No.11676119 Report

Quoted By: >>11676151

>>11676041
You made a mistake. It should be
(210+x)/(n+3) = 80 and (180+x)/(n+2) = 85, where x is anons current score and n is the current number of tests taken. Solving the system of equation will yield n = 8. like in >>11675915

Brainlet

Brainlet Fri 15 May 2020 18:04:40 No.11676139 Report

Quoted By:

>>11675744
Tfw I get n= -8/3

Anonymous

Anonymous Fri 15 May 2020 18:07:10 No.11676151 Report

Quoted By: >>11676164 >>11678131

>>11676119
im working under the assumption that the average for both cases is calculated after the third test.
my reasoning is that anon's desire is to be able to skip a test.

80n - 210 = current total score
85n -180 = current total score
80n - 210= 85n - 180
80n = 85n + 30
5n = -30
n = -6
n - 3 = current number of taken tests = -9

Anonymous

Anonymous Fri 15 May 2020 18:11:13 No.11676164 Report

Quoted By:

>>11676151
Well I can't argue with that logic. Carry on then, friend.

Anonymous

Anonymous Fri 15 May 2020 18:36:53 No.11676238 Report

Quoted By:

>>11675744
not enough information to determine the number of test anon has done

Anonymous

Anonymous Sat 16 May 2020 04:38:19 No.11677985 Report

Quoted By:

>>11675744
the answer is 8,it took me too long to figure our,i found the two values for both y and x,and then solved Y - Y = 0,what is the proper way to solve this system of equations,help a retard anon out.

Anonymous

Anonymous Sat 16 May 2020 05:13:49 No.11678027 Report

Quoted By: >>11678121

>>11675744
Let n = number of tests taken prior and x = the average score on those n tests

(nx + 2.1)/(n + 3) = .8
(nx + 1.8)/(n + 2) = .85

Solve for x in equation 1:
nx + 2.1 = .8n + 2.4
nx = .8n + .3
x = (.8n + .3) / n

Substitute the above for x into equation 2:
(n * ((.8n + .3) / n) + 1.8) / (n + 2) = .85
(.8n + .3 + 1.8) / (n + 2) = .85
(.8n + 2.1) / (n + 2) = .85
.8n + 2.1 = .85n + 1.7
.4 = .05n
n = 8

Anonymous

Anonymous Sat 16 May 2020 06:22:56 No.11678121 Report

Quoted By: >>11678133

>>11678027
>(nx + 2.1)/(n + 3) = .8
>multiplying the number of prior tests by the average score of prior tests
Isn't this wrong? Shouldn't it just be
>(x + 2.1)/(n + 3) = .8

Anonymous

Anonymous Sat 16 May 2020 06:33:38 No.11678131 Report

Quoted By:

>>11676041
>>11676151
>im working under the assumption that the average for both cases is calculated after the third test.
But OP's question is invalid if that were the case.
Assuming the third test counts as a zero, there's no way the 2nd average could equal 85, because the average after three tests would already be lower in the 2nd case than the first.

70% on 3 tests: 2.1 / 3 = 0.7 average over 3 tests
90% on 2 tests: 1.8 / 3 = 0.6 average over 3 tests

Anonymous

Anonymous Sat 16 May 2020 06:35:20 No.11678133 Report

Quoted By: >>11678159

>>11678121
No, remember what the average is in this problem: the total accumulated score divided by the number of tests taken. To get the total accumulated score, we can just move some variables around and calculate it by multiplying the average score (x) by the number of tests taken (n).

We don't know how many tests the anon took beforehand and we don't know what the average for those tests were. If I defined the result I wanted as just one variable, then I have no way of distinguishing between those 2 unknowns. In the way you defined it, n is actually part of x.

Anonymous

Anonymous Sat 16 May 2020 06:54:17 No.11678159 Report

Quoted By:

>>11678133
>the average score (x)
Ahh, that's right. I was confused because I used x for the total score, not the average.
(nx + 2.1)/(n + 3) = .8 works when x is the average, and
(x + 2.1)/(n + 3) = .8 works when x is the total score,
though both ultimately result in n = 8

Anonymous

Anonymous Sat 16 May 2020 13:27:31 No.11678731 Report

Quoted By: >>11678826

>>11676041
where do 210 and 180 come from?

Anonymous

Anonymous Sat 16 May 2020 14:15:14 No.11678826 Report

Quoted By:

>>11678731
just try to solve the equation anon,its not as hard as you think.

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