Advertisement

The letters of the word ‘RANDOM’ are arranged as in a dictionary. What is the rank of word ‘RANDOM’?


Numbers of letters in 'RANDOM' = (R → 1, A → 1, N → 1, D → 1, O → 1, M → 1) = 6
Number of words that begin with A = straight P presuperscript 1 subscript 1 cross times 5 factorial space equals space 1 cross times 120 space equals space 120
Number of words that begin with D = straight P presuperscript 1 subscript 1 cross times 5 factorial space equals space 1 space cross times space 120 space equals space 120
Number of words that begin with M = straight P presuperscript 1 subscript 1 cross times 5 factorial space equals space 1 cross times 120 equals 120
Number of words that begin with O = straight P presuperscript 1 subscript 1 cross times 5 factorial space equals space 1 cross times 120 equals 120
Number of words that begin with N = straight P presuperscript 1 subscript 1 cross times 5 factorial space equals space 1 cross times 120 equals 120
So far, we have formed 120 + 120 + 120 + 120 + 120 = 600 words.
Now words starting with R.
Number of words starting with RAD = 1 x 1 x 1 x 3! = 6.
Number of words starting with RAM = 1 x 1 x 1 x 3! = 6.
Total words                     = 600 + 12 = 612.
613th word is RANDMO
614th word is RANDOM
∴ Rank of the word random in a dictionary is 614. 

469 Views

Advertisement
In how many ways can 5 persons be seated around a round table so that two of them must always be together?

Tie the two 
Number of arrangements = space straight P presuperscript 2 subscript 2 space equals space 2 factorial space equals space 2
Mix with remaining
Now, we have 3 + 1 = 4 persons to sit around a round table.
The number of permutations = (4 - 1)! = 3! = 6
Hence, the total number of arrangments when the two persons sit together
                         = 2 x 6 = 12

 

105 Views

Find the number of words with or without which can be made using all the letters of the word ‘AGAIN’. If these words are written as in a dictionary, what will be the 50th word? 

Total letters in word 'AGAIN' (A → 2, G → 1, I → 1, N → 1) = 5
Number of words that begin with A = space space fraction numerator straight P presuperscript 2 subscript 2 over denominator 2 factorial end fraction cross times straight P presuperscript 4 subscript 4 space equals space 1 cross times 4 factorial space equals space 24
(Fix A at first place, so that the remaining 4 letters are different)

Number of words with begin with G = straight P presuperscript 1 subscript 1 space cross times space fraction numerator straight P presuperscript 4 subscript 4 over denominator 2 factorial end fraction space equals space 1 cross times fraction numerator 4 factorial over denominator 2 factorial end fraction equals 24 over 12 equals 12
Number of words that begin with I = straight P presuperscript 1 subscript 1 cross times fraction numerator straight P presuperscript 4 subscript 4 over denominator 2 factorial end fraction equals 12
Thus, so far we have formed 24 + 12 + 12 = 48 words.
The 49th word will begin with N and it is NAAGI and the 50th word is NAAIG.

107 Views

How many different words can be formed by using the letters of the word ‘ALLAHABAD?

(a) In how many of these do the vowels occupy even positions.

(b) In how many of these, the two L’s do not come together?


Number of letters in word 'ALLAHABAD' = (A → 4, L → 2, H → 1, B → 1, D → 1) = 9

Number of arrangements   = fraction numerator straight n factorial over denominator straight p factorial space straight q factorial end fraction space equals space fraction numerator 9 factorial over denominator 4 factorial space 2 factorial end fraction space equals space fraction numerator 9 cross times 8 cross times 7 cross times 6 cross times 5 over denominator 2 end fraction equals 7560.

(a) There are only four A's as vowels.

          

They can occupy even places (2, 4, 6, 8) in space space fraction numerator straight P presuperscript 4 subscript 4 over denominator 4 factorial end fraction  ways
∴   Number of ways in which vowels occupying even places = 1
We are left with 5 places and letters (L → 2, H → 1, B → 1, D → 1).

Number of permutations = fraction numerator 5 factorial over denominator 2 factorial end fraction space equals space 5 cross times 4 cross times 3 equals 60.
Hence, total number of arrangements in which A's occupy even places
                            = 1 x 60 = 60.

(b) We first find the number of arrangements in which two L's are not together:
      Number of arrangements in which two L's are together
                 equals fraction numerator straight P presuperscript 2 subscript 2 over denominator 2 factorial end fraction cross times fraction numerator straight P presuperscript left parenthesis 7 plus 1 right parenthesis end presuperscript subscript 7 plus 1 end subscript over denominator 4 factorial end fraction space equals space 1 cross times fraction numerator 8 factorial over denominator 4 factorial end fraction space equals space 8 cross times 7 cross times 6 cross times 5 space equals space 1680.
Hence, the number of arrangements in which the two L's are not together
     = (Total arrangements) - (the number of arrangements in which the two L's are together)
     = 7560 - 1680 = 5880.

526 Views

In how many ways can 8 students be seated

(a) in a straight line (b) in a circle?


n = 8

(a) Number of arrangements in a row = <pre>uncaught exception: <b>mkdir(): Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php at line #56mkdir(): Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php line 56<br />#0 [internal function]: _hx_error_handler(2, 'mkdir(): Permis...', '/home/config_ad...', 56, Array)
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php(56): mkdir('/home/config_ad...', 493)
#2 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/FolderTreeStorageAndCache.class.php(110): com_wiris_util_sys_Store->mkdirs()
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/RenderImpl.class.php(231): com_wiris_plugin_impl_FolderTreeStorageAndCache->codeDigest('mml=<math xmlns...')
#4 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(59): com_wiris_plugin_impl_RenderImpl->computeDigest(NULL, Array)
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#6 {main}</pre>

(b) Number of arrangements in circular formation = (n - 1)! = 7! = 5040.

181 Views

Advertisement