Solving math problem in EXCEL! Problem solved on paper.

[bilebizzare]

Hi guys, I've been using this forum for long time, but this is my first time posting .
Recently I got math problem to solve on job interview, which I did on paper, but problem is it was needed to be done in excel. Below is question and the way I did it on paper. Please help me solve it through excel.

[Class did test. If all boys had 3 points more, average points of whole class would increase for 1.2 points. What's the % of girls in class?]



X - boys P - points boys
Y - girls P1 - points girls

(X*P + Y*P1)/(X+Y) = AVERAGE
(X*P + Y*P1 + 3X)/(X+Y) = AVERAGE + 1.2
(X*P + Y*P1)/(X+Y) + 3X/(X+Y) = AVERAGE +1.2
3X/(X+Y) = 1.2
3X = 1.2X + 1.2Y

1.8X = 1.2Y
Y = (1.8/1.2)*X
Y = 1.5X

X+Y = 100%
X+1.5X = 100%
2.5X = 100%
X = 40%
Y=60%
% of girls in class is 60%!

 

[tyija1995]

In Excel you could use % girls is given by the following formula:
=1-100%/(3/1.2)
Because 100%/(3/1.2) would give you the % of boys, so 1-ANS gives % of girls.
3 comes from the fact as you say that each boy had 3 higher than each girl and 1.2 is the average increase.

 

[bilebizzare]

It makes sense, thank you very much!

 

[tyija1995]

Glad it helped!
You could advance on the formula above and put
=1-100%/(boysScore/averageScore)
where boysScore is a named range cell containing the improvement that the boys had (in this case = 3)
and averageScore also a named range cell that is how much the boys bumped up the average score (in this case = 1.2)
This would make the formula more dynamic so that if you had the average only go up by 0.6 in your example you can change 1 cell to change the entire output of the formula!
Ofcourse this is for a very specific scenario however, but interesting to know it can be done!
Good luck in your interview