Final answer:
To find the unknown number when the HCF and LCM are given, and one number is known, use the formula HCF × LCM = Number1 × Number2. After substituting the known values and solving for the unknown number, it is revealed that the other number is 12.
Step-by-step explanation:
The question asks to find the other number when the highest common factor (HCF) of two numbers is 4, and the least common multiple (LCM) is 120, given that one of the numbers is 40. Recall the relationship between two numbers (let's denote them A and B), their HCF, and their LCM: HCF × LCM = A × B. Using this, we can substitute the known values into this equation: 4 × 120 = 40 × B. Simplifying this, we get 480 = 40B. Further simplification by dividing both sides by 40 gives us B = 12.
Therefore, the other number we are seeking is 12.