MHB What is the Minimum Number of Friends Needed for Unique Dinner Invitations?

AI Thread Summary
To determine the minimum number of friends John needs for unique dinner invitations, the correct approach is to set the inequality as \(\binom{n}{3} \geq 365\). This leads to the equation \(\frac{(n-1)(n-2)n}{6} \geq 365\). The solution requires finding the smallest natural number \(n\) that satisfies this inequality. It is noted that \(\binom{14}{3} = 364\), indicating that at least 14 friends are necessary. Thus, John needs a minimum of 14 friends to ensure he can invite different triplets each evening without repetition.
Lancelot1
Messages
26
Reaction score
0
Hello all,

I am trying to solve this one:

John has n friends . He wants to invite in each evening (365 days a year) three of his friends for dinner. What should be the size of n, such that it will be possible not to invite the same triplet twice ?

What I did was:

\[\binom{n}{3}\leq 365\]

which turns into:

\[\frac{(n-1)(n-2)n}{6}\leq 365\]

I have tried to solve it, manually and with a mathematical software, in both ways n was not a natural number...where is my mistake ?
 
Mathematics news on Phys.org
Lancelot said:
I have tried to solve it, manually and with a mathematical software, in both ways n was not a natural number
First, the inequality should be $\binom{n}{3}\ge365$. Second, the answer to this problem is an inequality $n\ge\ldots$, not a specific value of $n$. For the lower bound of $n$ take the smallest natural number that is equal to or larger than the root of that equation. Note that $\binom{14}{3}=364$.
 
Suppose ,instead of the usual x,y coordinate system with an I basis vector along the x -axis and a corresponding j basis vector along the y-axis we instead have a different pair of basis vectors ,call them e and f along their respective axes. I have seen that this is an important subject in maths My question is what physical applications does such a model apply to? I am asking here because I have devoted quite a lot of time in the past to understanding convectors and the dual...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...

Similar threads

Replies
3
Views
2K
Replies
4
Views
4K
Replies
13
Views
3K
Replies
5
Views
3K
Replies
1
Views
4K
Replies
5
Views
4K
Back
Top