Permutations and Combinations
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New answer posted
a month agoContributor-Level 10
Let xyz be the three digit number
x+y+z=10, x≥1, y≥0, z≥0
x-1=t => x=1+t, x-1≥0
t≥0
t+y+z = 10-1
t+y+z=9, 0≤t, y, z≤9
total number of non negative integral solution =? ³? ¹C? = ¹¹C? = (11*10)/2 = 55
But for t=9, x=10, so required number or integers = 55-1=54
New question posted
a month agoNew answer posted
a month agoContributor-Level 10
MOTHER
1? E
2? H
3? M
4? O
5? R
6? T
So position of word MOTHER in dictionary
2*5!+2*4!+3*3!+2!+1
=240+48+18+2+1
=309
New answer posted
a month agoContributor-Level 10
Family of planes: x+y+z+1+? (2x-y+z+3)=0. Parallel to line means dot product of normals is zero.
New answer posted
a month agoContributor-Level 9
| Class | No. of students | Number of possible cases |
| :-: | :-: | :- |
| 10 | 5 | (I) 2 | (II) 3 | (III) 2 |
| 11 | 6 | (I) 2 | (II) 2 | (III) 3 |
| 12 | 8 | (I) 6 | (II) 5 | (III) 5 |
Total cases =? C? *? C? *? C? +? C? *? C? *? C? +? C? *? C? *? C?
= 23,800 = 100K
∴ K = 238
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