If $a_1, a_2, \ldots a_n$ are $n$ distinct odd natural numbers not divisible by any prime greater th

Question

If $a_1, a_2, \ldots a_n$ are $n$ distinct odd natural numbers not divisible by any prime greater than 5 , then $\frac{1}{a_1}+\frac{1}{a_2}+\ldots+\frac{1}{a_n}$ is less than

Professor PC Thomas Classes · Answer

Sum of reciprocals generated by $(1+1/3+1/3^2\dots)(1+1/5+1/5^2\dots) = \frac{1}{1-1/3} \frac{1}{1-1/5} = \frac{3}{2} 	imes \frac{5}{4} = \frac{15}{8}$.