If 'a', 'b' are the 2 positive divisors of N & if (N - a) = 270 & (N - b) = 280, then a > b or in other words a = b + 10

a = N - 270 & b = N - 280, which means N has to start from 280 for 'a' & 'b' to be positive.

285(N) is divisible by 15(a) & 5(b) ====> 15*19 & 5*57 ====> LCM = 15 < 285

288(N) is divisible by 18(a) & 8(b) ====> 18*16 & 8*36 ====> LCM = 72 < 288

300(N) is divisible by 30(a) & 20(b) ====> 30*10 & 20*30 ====> LCM = 60 < 300

315(N) is divisible by 45(a) & 35(b) ====> 45*7 & 35*9 ====> LCM = 315 = 315

are **4 instances** for which the above conditions held true. This is partly because as 'a' and 'b' becomes bigger compared to 'N', 'a' and 'b' stop having an LCM lesser than N. In other words 'a' & 'b' will not divide 'N' simultaneously.