There are three brothers. The sums of ages of two of them at a time are 4 years, 6 years and 8 years. The age difference between the eldest and the youngest is

Consider the following in respect of natural numbers a, b and c :

1. LCM (ab, ac) =a LCM( b, c)
2. HCF (ab, ac) = a HCF (b, c)
3. HCF (a, b) < LCM (a, b)
4. HCF (a, b) divides LCM (a,b).

Which of the above are correct

The value of k, for which the system of equations 3x-ky-20=0 and 6x-10y+40 = 0 has no solution, is

Which of the points P(5,-1), Q(3,-2), and R(1,1) lie in the solution of the system of inequations x+y≤4 and x-y≥2

The solution of the inequation 

1+1/x-1/x²≥0

is (given that x≠ 0)

Consider the following statements :

1. There exists a positive real number m such that cosx = 2^m+1
2. mn ≥ m+n for all m, n belonging to set of natural numbers.

Which of the above statements is / are correct