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Question

Which of the following expresses the prime factorisation of 54?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$3 \times 3 \times 3 \times 2$

Prime Factorisation of 54: Step-by-Step

Prime factorisation means expressing a number as a product of its prime factors. Prime numbers are numbers greater than 1 that have only two divisors: 1 and themselves.

Calculating Prime Factors for 54

We find the prime factors of 54 by dividing by the smallest prime numbers possible:

  • Divide 54 by the smallest prime number, 2: $54 \div 2 = 27$
  • Now, factor 27. It is not divisible by 2. The next prime is 3: $27 \div 3 = 9$
  • Factor 9. It is divisible by 3: $9 \div 3 = 3$
  • The last factor, 3, is a prime number.

So, the prime factorisation of 54 is $2 \times 3 \times 3 \times 3$. The order might differ, but the factors remain the same.

Evaluating Number Factorisation Options

We check each provided option to see which one represents the prime factorisation of 54:

  • Option 1: $5.4 \times 10 = 54$. This is not a prime factorisation because 10 is not a prime number and 5.4 is not an integer prime factor.
  • Option 2: $3 \times 3 \times 6 = 54$. This is incorrect because 6 is not a prime number.
  • Option 3: $9 \times 6 = 54$. This is incorrect because neither 9 nor 6 are prime numbers.
  • Option 4: $3 \times 3 \times 3 \times 2 = 54$. All the factors (3 and 2) are prime numbers. This correctly represents the prime factorisation of 54.

The expression $3 \times 3 \times 3 \times 2$ accurately shows the prime factors of 54.

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Important Questions from Multiples and Factors

  1. Express 486 as a product of powers of prime factors.

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