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Permutation and CombinationQuestion and Answers: Page 3

Question Number 189614 Answers: 1 Comments: 0

Question Number 189049 Answers: 1 Comments: 2

Question Number 189021 Answers: 2 Comments: 4

How many non−similar triangles have integer angles in °?

$${How}\:{many}\:{non}−{similar}\:{triangles} \\ $$$${have}\:{integer}\:{angles}\:{in}\:°? \\ $$

Question Number 188551 Answers: 1 Comments: 0

you randomly select a 5 digit number. what′s the probability that this number has exactly 3 different digits?

$${you}\:{randomly}\:{select}\:{a}\:\mathrm{5}\:{digit}\:{number}. \\ $$$${what}'{s}\:{the}\:{probability}\:{that}\:{this}\:{number} \\ $$$${has}\:{exactly}\:\mathrm{3}\:{different}\:{digits}? \\ $$

Question Number 188362 Answers: 2 Comments: 0

find the number of 5 digit natural numbers with strictly ascending digits whose sum is 20. example: 12458 is such a number

$${find}\:{the}\:{number}\:{of}\:\mathrm{5}\:{digit}\:{natural} \\ $$$${numbers}\:{with}\:{strictly}\:{ascending}\: \\ $$$${digits}\:{whose}\:{sum}\:{is}\:\mathrm{20}. \\ $$$${example}:\:\mathrm{12458}\:{is}\:{such}\:{a}\:{number} \\ $$

Question Number 188301 Answers: 1 Comments: 4

Find the number of triangles with integer side lengths and perimeter p.

$${Find}\:{the}\:{number}\:{of}\:{triangles}\:{with} \\ $$$${integer}\:{side}\:{lengths}\:{and}\:{perimeter}\:{p}. \\ $$

Question Number 187948 Answers: 1 Comments: 0

Given a set H={1,2,3,...,300. We will a create a subset of H consisting of three elements. If the sum of the three elements is divisible by 3 then the number of subsets that canbe made is x. Find the remainder if x is divided by 100000

$$ \\ $$$$\mathrm{Given}\:\mathrm{a}\:\mathrm{set}\:\mathrm{H}=\left\{\mathrm{1},\mathrm{2},\mathrm{3},...,\mathrm{300}.\:\mathrm{We}\:\mathrm{will}\:\mathrm{a}\right. \\ $$$$\mathrm{cre}{a}\mathrm{te}\:\mathrm{a}\:\mathrm{subset}\:\mathrm{of}\:\mathrm{H}\:\mathrm{consisting}\:\mathrm{of}\: \\ $$$$\mathrm{thre}{e}\:\mathrm{elements}.\:\mathrm{If}\:\mathrm{the}\:\mathrm{sum}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{thr}{e}\mathrm{e}\:\mathrm{elements}\:\mathrm{is}\:\mathrm{divisible}\:\mathrm{by}\:\mathrm{3}\:\: \\ $$$$\mathrm{then}\:\mathrm{the}\:\mathrm{number}\:\mathrm{of}\:\mathrm{subsets}\:\mathrm{that}\: \\ $$$$\mathrm{canbe}\:\mathrm{made}\:\mathrm{is}\:\mathrm{x}.\:\mathrm{Find}\:\mathrm{the} \\ $$$$\mathrm{remaind}{e}\mathrm{r}\:\mathrm{if}\:\mathrm{x}\:\mathrm{is}\:\mathrm{divided}\:\mathrm{by}\:\mathrm{100000} \\ $$

Question Number 185659 Answers: 1 Comments: 1

prove for r, n ∈ N Σ_(k=r) ^n ((k),(r) ) = (((n+1)),((r+1)) ) (Hockey−stick identity)

$${prove}\:{for}\:{r},\:{n}\:\in\:\mathbb{N} \\ $$$$\underset{{k}={r}} {\overset{{n}} {\sum}}\begin{pmatrix}{{k}}\\{{r}}\end{pmatrix}\:=\begin{pmatrix}{{n}+\mathrm{1}}\\{{r}+\mathrm{1}}\end{pmatrix} \\ $$$$\left({Hockey}−{stick}\:{identity}\right) \\ $$

Question Number 185642 Answers: 1 Comments: 1

Question Number 185350 Answers: 0 Comments: 1

C_4 ^4 +C_4 ^5 +C_4 ^6 +...+C_4 ^(26) =?

$$\:\:\:{C}_{\mathrm{4}} ^{\mathrm{4}} +{C}_{\mathrm{4}} ^{\mathrm{5}} +{C}_{\mathrm{4}} ^{\mathrm{6}} +...+{C}_{\mathrm{4}} ^{\mathrm{26}} \:=? \\ $$

Question Number 182793 Answers: 0 Comments: 0

Suppose now that Allie is actually 70 years old, and that her life expectancy (if cured) is 12 years rather than 20 . Which procedure now has the greather expected value ? What if her life expectancy is 8 years?

$$\:{Suppose}\:{now}\:{that}\:{Allie}\:{is}\:{actually} \\ $$$$\mathrm{70}\:{years}\:{old},\:{and}\:{that}\:{her}\:{life}\:{expectancy} \\ $$$$\left({if}\:{cured}\right)\:{is}\:\mathrm{12}\:{years}\:{rather}\:{than} \\ $$$$\mathrm{20}\:.\:{Which}\:{procedure}\:{now}\:{has}\:{the} \\ $$$${greather}\:{expected}\:{value}\:?\:{What}\:{if}\:{her} \\ $$$${life}\:{expectancy}\:{is}\:\mathrm{8}\:{years}? \\ $$

Question Number 182695 Answers: 1 Comments: 2

If two events A and B are such that P(A^c )=0.3 ; P(B)=0.4 and P(A∩B^c )= 0.5 then P((B/(A∪B^c )))=? (A) 0.20 (B) 0.25 (C) 0.30 (D) 0.35

$$\:\:\mathrm{If}\:\mathrm{two}\:\mathrm{events}\:\mathrm{A}\:\mathrm{and}\:\mathrm{B}\:\mathrm{are}\:\mathrm{such}\: \\ $$$$\:\:\mathrm{that}\:\mathrm{P}\left(\mathrm{A}^{\mathrm{c}} \right)=\mathrm{0}.\mathrm{3}\:;\:\mathrm{P}\left(\mathrm{B}\right)=\mathrm{0}.\mathrm{4}\:\mathrm{and} \\ $$$$\:\:\mathrm{P}\left(\mathrm{A}\cap\mathrm{B}^{\mathrm{c}} \right)=\:\mathrm{0}.\mathrm{5}\:\mathrm{then}\:\mathrm{P}\left(\frac{\mathrm{B}}{\mathrm{A}\cup\mathrm{B}^{\mathrm{c}} }\right)=? \\ $$$$\:\left(\mathrm{A}\right)\:\mathrm{0}.\mathrm{20}\:\:\:\:\:\:\left(\mathrm{B}\right)\:\mathrm{0}.\mathrm{25}\:\:\:\:\:\:\left(\mathrm{C}\right)\:\mathrm{0}.\mathrm{30}\:\:\:\:\:\:\left(\mathrm{D}\right)\:\mathrm{0}.\mathrm{35} \\ $$$$\:\: \\ $$

Question Number 181971 Answers: 1 Comments: 0

How many words can be formed from different letters of the “Your answer is wrong” with not repeating? So that they shouldn′t start with ′o′ neither ′w′ and shouldn′t end with ′w′, and should be′r′ & ′s′ adjacents. Oya...n, Wen...y, Iog...w , Yourws...e : are invalid Enrsow...g : is valid Q.180162

$${How}\:{many}\:{words}\:{can}\:{be}\:{formed}\:{from}\:{different} \\ $$$${letters}\:{of}\:{the}\:``{Your}\:{answer}\:{is}\:{wrong}''\:{with}\:{not} \\ $$$${repeating}?\:{So}\:{that}\:{they}\:{shouldn}'{t}\:{start}\:{with}\:'{o}'\: \\ $$$$\:{neither}\:'{w}'\:{and}\:{shouldn}'{t}\:{end}\:{with}\:'{w}',\:{and} \\ $$$$\:{should}\:{be}'{r}'\:\&\:'{s}'\:{adjacents}. \\ $$$$ \\ $$$$\:\cancel{{O}ya}...{n},\:\cancel{{W}en}...{y},\:{Iog}...\cancel{{w}}\:,\:{You}\cancel{{r}w}\cancel{{s}}...{e}\:\::\:{are}\:{invalid} \\ $$$$\:{Enrsow}...{g}\::\:{is}\:{valid} \\ $$$${Q}.\mathrm{180162} \\ $$

Question Number 181939 Answers: 2 Comments: 0

If 10 different balls are to be placed in 4 boxes at random , then the probability that two of these boxes contain exactly 2 and 3 balls

$${If}\:\mathrm{10}\:{different}\:{balls}\:{are}\:{to}\:{be}\:{placed} \\ $$$${in}\:\mathrm{4}\:{boxes}\:{at}\:{random}\:,\:{then}\:{the}\:{probability} \\ $$$${that}\:{two}\:{of}\:{these}\:{boxes}\:{contain} \\ $$$${exactly}\:\mathrm{2}\:{and}\:\mathrm{3}\:{balls}\: \\ $$

Question Number 181251 Answers: 1 Comments: 1

Question Number 180890 Answers: 0 Comments: 2

We have 7 sets with 2 subsets each (yes and no are the 2 subsets of each of the 7 sets) how many possible combinations are there if one of the subset is picked for each of the 7 sets.

Question Number 180899 Answers: 1 Comments: 0

H_n = Σ_(k=1) ^n (1/k) show that H_(2n) − H_n = Σ_(k=1) ^n ((1/(2k−1))−(1/(2k)))

$${H}_{{n}} \:=\:\underset{{k}=\mathrm{1}} {\overset{{n}} {\sum}}\frac{\mathrm{1}}{{k}} \\ $$$${show}\:{that}\:{H}_{\mathrm{2}{n}} \:−\:{H}_{{n}} \:=\:\underset{{k}=\mathrm{1}} {\overset{{n}} {\sum}}\left(\frac{\mathrm{1}}{\mathrm{2}{k}−\mathrm{1}}−\frac{\mathrm{1}}{\mathrm{2}{k}}\right) \\ $$

Question Number 180773 Answers: 1 Comments: 0

How many triangles can be formed from non−adjacent vertices of a regular polygon that it angle is 177^( °) ?

$${How}\:{many}\:{triangles}\:{can}\:{be}\:{formed}\:{from} \\ $$$$\:{non}−{adjacent}\:{vertices}\:{of}\:{a}\:{regular}\:{polygon} \\ $$$$\:{that}\:{it}\:{angle}\:{is}\:\mathrm{177}^{\:°} \:? \\ $$

Question Number 180585 Answers: 2 Comments: 0

there are 5 points on a line and 4 points on a parallel line. how many quadrilaterals can be formed with these points as vertrices?

$${there}\:{are}\:\mathrm{5}\:{points}\:{on}\:{a}\:{line}\:{and}\:\mathrm{4}\: \\ $$$${points}\:{on}\:{a}\:{parallel}\:{line}. \\ $$$${how}\:{many}\:{quadrilaterals}\:{can}\:{be}\: \\ $$$${formed}\:{with}\:{these}\:{points}\:{as}\: \\ $$$${vertrices}? \\ $$

Question Number 180520 Answers: 2 Comments: 0

The number of triangles that can be formed by 5 points in a line and 3 points on a parralel line is ___

$$\:\:\:\mathrm{The}\:\mathrm{number}\:\mathrm{of}\:\mathrm{triangles}\: \\ $$$$\:\:\:\mathrm{that}\:\mathrm{can}\:\mathrm{be}\:\mathrm{formed}\:\mathrm{by}\:\mathrm{5}\:\mathrm{points}\: \\ $$$$\:\:\:\mathrm{in}\:\mathrm{a}\:\mathrm{line}\:\mathrm{and}\:\mathrm{3}\:\mathrm{points}\:\mathrm{on}\:\mathrm{a}\:\mathrm{parralel}\:\mathrm{line} \\ $$$$\:\:\:\mathrm{is}\:\_\_\_\: \\ $$

Question Number 180421 Answers: 2 Comments: 0

find the number of numbers less than 10^6 which contain at least 3 different digits.

$${find}\:{the}\:{number}\:{of}\:{numbers}\:{less}\:{than}\: \\ $$$$\mathrm{10}^{\mathrm{6}} \:{which}\:{contain}\:{at}\:{least}\:\mathrm{3}\:{different} \\ $$$${digits}. \\ $$

Question Number 180335 Answers: 2 Comments: 1

The integers between 1 to 10^4 contain exactly one 8 and one 9 is? I got 1160 but one is arguing 1154only..kindly help me out

$${The}\:{integers}\:{between}\:\mathrm{1}\:{to}\:\mathrm{10}^{\mathrm{4}} \\ $$$${contain}\:{exactly}\:{one}\:\mathrm{8}\:\:{and}\:{one}\:\mathrm{9} \\ $$$${is}?\:{I}\:{got}\:\mathrm{1160}\:{but}\:{one}\:\:{is}\:{arguing} \\ $$$$\mathrm{1154}{only}..{kindly}\:{help}\:{me}\:{out} \\ $$

Question Number 180212 Answers: 1 Comments: 0

How many polygons can be formed from a heptagon?

$${How}\:{many}\:{polygons}\:{can}\:{be}\:{formed} \\ $$$$\:{from}\:{a}\:{heptagon}?\: \\ $$

Question Number 180027 Answers: 1 Comments: 0

There are 4 identical mathematics books, 3 identical physics books, 2 identical chemistry books and 2 identical biology books. in how many ways can you compile these books such that same books are not mutually adjacent. (an unsolved old question)

$$\mathrm{There}\:\mathrm{are}\:\mathrm{4}\:\mathrm{identical}\:\mathrm{mathematics} \\ $$$$\mathrm{books},\:\mathrm{3}\:\mathrm{identical}\:\mathrm{physics}\:\mathrm{books},\:\mathrm{2} \\ $$$$\mathrm{identical}\:\mathrm{chemistry}\:\mathrm{books}\:\mathrm{and}\:\mathrm{2} \\ $$$$\mathrm{identical}\:\mathrm{biology}\:\mathrm{books}.\:\mathrm{in}\:\mathrm{how}\:\mathrm{many} \\ $$$$\mathrm{ways}\:\:\mathrm{can}\:\mathrm{you}\:\mathrm{compile}\:\mathrm{these}\:\mathrm{books} \\ $$$$\mathrm{such}\:\mathrm{that}\:\mathrm{same}\:\mathrm{books}\:\mathrm{are}\:\mathrm{not}\:\mathrm{mutually} \\ $$$$\mathrm{adjacent}. \\ $$$$\left({an}\:{unsolved}\:{old}\:{question}\right) \\ $$

Question Number 179993 Answers: 0 Comments: 13

How many 6 digit numbers have different digits and are divisible by 11? (an unsolved old question)

$${How}\:{many}\:\mathrm{6}\:{digit}\:{numbers}\:{have} \\ $$$${different}\:{digits}\:{and}\:{are}\:{divisible}\:{by} \\ $$$$\mathrm{11}? \\ $$$$\left({an}\:{unsolved}\:{old}\:{question}\right) \\ $$

Question Number 179818 Answers: 4 Comments: 0

in how many ways can you distribute 20 different books to 5 students such that each student gets at least 2 books?

$${in}\:{how}\:{many}\:{ways}\:{can}\:{you}\:{distribute} \\ $$$$\mathrm{20}\:{different}\:{books}\:{to}\:\mathrm{5}\:{students}\:{such} \\ $$$${that}\:{each}\:{student}\:{gets}\:{at}\:{least}\:\mathrm{2}\:{books}? \\ $$

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