Latest Elitmus Aptitude Question SOLUTION: 1/a + 1/b = 1/c All are Positive integer and a is a Prime Number greater than 2 then how many Possible combination of (a,b)?? a)0 b)1 c)2 d)4

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(#M40034171) ELITMUS Numerical Ability question Number System Keep an EYE

1/a + 1/b = 1/c All are Positive integer and a is a Prime Number greater than 2 then how many Possible combination of (a,b)??
a)0
b)1
c)2
d)4

Asked In Elitmus tausif (10 years ago)

Unsolved Read Solution (8)

Is this Puzzle helpful?   (7)   (2) Submit Your Solution Permutation and Combination

Read Solution (8) :

PANKAJ KUMAR  (10 years ago)

solution must be 4..
psssible combination is (3,6),(5,20),(7,42)....

Is this solution Helpfull? Yes (14) | No   

pawan  (9 years ago)

1/a+1/b=1/c..............// a,b,c are +v integer
(b+a)/ab=1/c.....
c(b+a)=ab.......
c=ab/(a+b)........
now we have to chose a&b such that ab ie. product of no when divide by sum of no give a integer value...
let a&b is
(3,6)..............3*6/3+6=+I...............3+6 which is square of 3
(5,20).............5*20/5+20=+I.............5+20........square of 5
(7,42).............7*42/7+42=+I.............7+42........square of 7
(11,b).............11*b/11+b=+I.............11+110.......square of 11=121 hence b=121-11=110
(13,b).............
(17,b).............
hence so on we get many no of solution...but options are 0,1,2,4....so we opt maximum one so ans is...(d)4

Is this solution Helpfull? Yes (13) | No (1)  

komal pandhariwal  (10 years ago)

For every prime a other than 2 .. b should be (a-1)*a
eg 1/3+1/6=1/2 ND SO ON FOR ALL THE PRIME NO.S

Is this solution Helpfull? Yes (5) | No (1)  

ankit sachdea  (10 years ago)

combination are more than 4
(3,6);(5,20);(7,42);(11,110);(13,156);(19,342).....

Is this solution Helpfull? Yes (1) | No   

arpit jain  (10 years ago)

B is the answer..since only prime number for 'a' greater than 2 satisfying above equation is 3..so 1/c - 1/b = 1/3..hence solving it we get c = 2 and b = 6..hence only pair formed is (3,6)

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utkarsh gupta  (10 years ago)

For every set of two prime no. Let a=3 b=5 there will only one c solution..here it will be 15/8.. by putting every set of prime no. In the equation answer will be different for all the combinations.so can be observed only one solution ans.b) 1

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nishant  (9 years ago)

what about c here

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Alkashree Jha  (9 years ago)

a,b are prime no. and greatr than 2
a=3,b=5
so combination posible is 2

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