Here's a math problem that most won't get correct

[levistep]

Taken from my actual SAT I took a long time ago.

The average (arithmetic mean) of a set of 6 numbers was 30. When one of the 6 numbers was removed from the set, the average decreased by 3. What was the number that was removed? For extra credit, show the algebraic equation.

 

[TomorrowsNewspaper]

45

 

[Journeyman]

45 , but if that was it , it was too easy, what's the catch?

unless I'm reading the question wrong.

 

[levistep]

45 , but if that was it , it was too easy, what's the catch?

unless I'm reading the question wrong.

You guessed and checked though, right? Anyone can do that and spend 3-5 minutes for each problem, but you only have about 45 seconds on the test per problem.

 

[gynecologist]

No algebraic equation shown by anyone yet..

 

[levistep]

No algebraic equation shown by anyone yet..

Of course not, in the future i'll make the numbers so large that you can't just guess and check.

 

[Journeyman]

I didn't guess I simply realized this in my head...that was pretty simple. You have 30X6 =180
than you have 27X5= 135 and you subract 135 from 180= 45.

 

[quantumleap]

45

Correct.

Let X be the missing number and Y equal the sum of the rest of the numbers.

If the average of 6 numbers is 30 then the sum of all 6 numbers is 180 which can be represented as:

X + Y = 180

Now if X is subtracted from the lot and the average of the rest of the numbers goes down 3, then the average of the rest of the 5 numbers is 27 and the total of the sum of the rest of the numbers is:

27 * 5 = 135

Now the sum of the rest of the numbers is equal to Y, so Y = 135.

Therefore:

X + Y = 180 would give us

X + 135 = 180

and subtracting 135 from both sides would give us

X + 135 - 135 = 180 - 135

which is equal to

X = 180 -135 = 45

 

[TomorrowsNewspaper]

simple math, no algebraic equations needed.

6 x 30 = 180
5 x 27 = 135

180-135 = 45

 

[levistep]

Good job everyone. Nobody can figure out the profit from the sale of a chicken but everyone figures this one out instantly. I can't bring this weak game to the RR anymore, forgive me.

The way I did it was (180-x)/5 = 27

 

[GreenDoberman]

Actually the correct algebraic formula would be:

(m1-m2) x (n-1) + m1

mean 1 less mean 2 times the original number less one(or the leftover number) added back into the original mean


Using this if we said we had 7 numbers with a mean of 35 and we took away one and got a mean of 30, what would be the number we removed?

(35-30) x (7-1) +35

5X6= 30 +35= 65

Your welcome to do it the long way to check it if you like.

 

[gynecologist]

Yeah good job guys..

 

[GreenDoberman]

You should use smaller numbers when multiplying or dividing and larger when adding or subtracting. Formulas are predicated on trying to get prime numbers since our brain is wired to only know up to 12 X 12, or our times tables.

 

[goodcall]

Taken from my actual SAT I took a long time ago.

The average (arithmetic mean) of a set of 6 numbers was 30. When one of the 6 numbers was removed from the set, the average decreased by 3. What was the number that was removed? For extra credit, show the algebraic equation.

Let 'y' represent the sum of the 5 numbers in both sets. Let 'x' be the number removed from the first set.

(y+x)/6=30
y/5=27

y+x=180
y=135

135+x=180

x=45

 

[rgorr]

the point is not practicality but the ability to think and problem solve - that is what universities want!!

 

[roach23]

When the the RR get filled with Math dorks. This shit is gay.

http://youporn.com/watch/517

 

[5starbomb]

45 thats easy

 

[Journeyman]

When the the RR get filled with Math dorks. This shit is gay.

http://youporn.com/watch/517

I hope the entire forum is filled with math dorks, if a sports gambler can't figure out that basic problem they have no business making bets.

lol 40 is the new 20, Dsethi, you better live it up now ! getting near 40 absolutely sucks:WTF:

 

[levistep]

good job guys. you've figured out a math problem that has little practicality in the real world, yet helps all of us 21+ year old men gain admission into college. That's good.

I'm more proud that I can calculate tips based on various common percentages than I am by doing this math problem. Who cares?

Good job fellas, get that entrance into MIT or Yale. Someone post a practical math problem.

the point is not practicality but the ability to think and problem solve - that is what universities want!!

Not only that, but if you are able to solve these problems then you'll be able to do real life math problems. Either way, why are you hating Dsethi? I bet you got like a 1500+ on the SAT, but you want to seem cool by bashing on it.

 

[Journeyman]

hate is in many a poster's nature it seems..I really have never understood why that is...it seems 8/10 posters would rather see a fellow poster fail or look bad, and is ready to pounce if they think they have.