- A30
- B45
- C180
- D90
Step-by-Step Solution
Multiply the primes back together: . The traps: 30 comes from using the 3 only once, 45 from dropping the 2 altogether, and 180 from using the 2 twice.
Answer: D) 90
A number has the prime factorisation . What is the number?
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Key idea: Prime vs composite
A whole number greater than 1 is **prime** if it has exactly two factors: 1 and itself. It is **composite** if it has more than two factors. The number 1 is neither prime nor composite (it has only one factor — itself). 2 is the only **even** prime; every other even number is divisible by 2 and so has at least three factors.
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