9000141505
Level:
B
Assuming \(x\in \mathbb{N}\),
find the solution set of the following equation.
\[
\frac{(x + 2)!}
{x!} = 2\cdot \frac{x!}
{(x - 2)!} + 3!
\]
\(\{4\}\)
\(\{4,1\}\)
\(\{1\}\)
Combinatorics
9000141506
Level:
B
Assuming \(x\in \mathbb{N}\),
find the solution set of the following equation.
\[
\left({11\above 0.0pt
4} \right) =\left ({11\above 0.0pt
x} \right)
\]
\(\{4,7\}\)
\(\{4\}\)
\(\{ - 4\}\)
9000141507
Level:
B
Assuming \(x,y\in \mathbb{N}\),
find the solution set of the following equation.
\[
\left({x\above 0.0pt
y}\right)^{2} - 2\cdot \left({x\above 0.0pt
y}\right) - 3 = 0
\]
\(\{[3,1],[3,2]\}\)
\(\{[3,1]\}\)
\(\{[3,1],[1,3]\}\)
9000141509
Level:
B
Assuming \(x\in \mathbb{N}\),
find the solution set of the following inequality.
\[
2\cdot \left({x - 1\above 0.0pt
x - 3}\right) + x\cdot (x - 9)\leq - 8
\]
\(\{3,4,5\}\)
\(\{1,2,3,4,5\}\)
\([ 1,5] \)
9000140503
Level:
B
Simplify for \(n\in \mathbb{N}\).
\[
\frac{(n + 1)! + (n - 1)!}
{n!}
\]
\(\frac{n^{2}+n+1}
{n} \)
\(2\)
\(n^{2} - 1\)
\(\frac{n^{2}-n+1}
{n} \)
9000140505
Level:
B
Simplify \(\frac{72!}
{70!+71!}\).
\(71\)
\(72\)
\(\frac{72}
{141}\)
\(\frac{72!}
{141!}\)
9000139301
Level:
A
Five different pieces of fruit are there on the plate. In how many ways it is possible
to distribute them into five children, if each child should have one piece?
\(120\)
\(100\)
\(140\)
\(160\)
9000139304
Level:
A
Find the number of possibilities how to choose a pair of timekeepers for a sport event if
there are \(50\)
candidates available for this job.
\(\frac{50!}
{2!\, 48!} = 1\:225\)
\(\frac{50}
{2} = 25\)
\(50^{2} = 2\:500\)
\(\frac{50!}
{48!} = 2\:450\)
9000139302
Level:
A
The phone number contains nine digits. A witness does not remember
the full number, but he remembers that the phone number starts by
\(728\), ends
by \(01\)
and there is no repeating digit in the number. How many phone numbers meet these
conditions?
\(120\)
\(320\)
\(520\)
\(720\)
9000139305
Level:
A
There are five rooms with three beds and one room with five beds in a hotel. A group of
\(20\)
people booked rooms at this hotel. Determine the number of possible choices for the
people to the five-bed room.
\(\frac{20!}
{5!\, 15!}=15\:504\)
\(20\cdot 3\cdot 5=300\)
\(\frac{20!}
{3!\, 5!}=3\:379\:030\:566\:912\:000\)
\(20^{5}=3\:200\:000\)