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

• solution must be 4..
  psssible combination is (3,6),(5,20),(7,42)....
• 10 years agoHelpfull: Yes(14) No(0)
• 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
• 10 years agoHelpfull: Yes(13) No(1)
• 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
• 10 years agoHelpfull: Yes(5) No(1)
• combination are more than 4
  (3,6);(5,20);(7,42);(11,110);(13,156);(19,342).....
• 10 years agoHelpfull: Yes(1) No(0)
• 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)
• 10 years agoHelpfull: Yes(0) No(4)
• 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
• 10 years agoHelpfull: Yes(0) No(2)
• what about c here
  
• 10 years agoHelpfull: Yes(0) No(2)
• a,b are prime no. and greatr than 2
  a=3,b=5
  so combination posible is 2
• 10 years agoHelpfull: Yes(0) No(2)