Is (50+5n)/n^2 an integer?
(1) n/5 is a positive integer
(2) n/10 is a positive integer
(i) Checking for n/5 being a positive integer.
Let n/5 = k
=> n = 5k
now replacing n = 5k in the original equation.
We get, (50 + 5(5k))/25k^2
=> (50 + 25k)/25k^2
Now on splitting the numberator => (50/25k^2) + (25k/25k^2)
=> 2/k^2 + 1/k
(Not sufficient as we have k in the denominator.)
(ii) Now checking for n/10 being a positive integer.
Let n/10 = k
=> n = 10k
now replacing n = 10k in the original equation.
We get, (50 + 5(10k))/100k^2
=> (50 + 50k)/100k^2
Now on splitting the numberator => (50/100k^2) + (50k/100k^2)
=> 1/2k^2 + 1/2k
(Not sufficient as we have k in the denominator.)
And as per (ii) n is divisible by 10 which means it is already divisible by 5 means both equations together are also insufficient.Hence ans is [E] :D ___________
Please drop in a kudos if it makes sense to you!