Since LCM is 2^3 x 3^2 x 5, the unknown number must have 2^3. Since HCF is 2^2 x 3, the unknown number must have a 3. Hence, we have 2^3 x 3 = 2x2x2x3. Since LCM has 3x3, So the unknown can have max two 3. We have 2x2x2x3x3. Since LCM has 5, the unknow number can have max one 5.