Paper 22 Q2IGCSE 0580 May/June 2023

Question

2 There are two prime numbers in this list. 27 47 57 61 75 93 Work out the sum of these two prime numbers.

This question tests your ability to identify prime numbers from a list of integers. A prime number is a number greater than 1 that has exactly two factors: 1 and itself.

Step-by-Step Solution

Key Takeaway

To check if a number is prime, you only need to test for factors up to its square root.

Common Mistakes

Thinking 57 is prime without checking if it's divisible by 3 (57 ÷ 3 = 19)
Missing that 27 and 93 are both multiples of 3 by not checking the sum of their digits

Exam Tip

For numbers ending in odd digits, always check divisibility by 3 by adding the digits together - if the sum is divisible by 3, the original number is too.

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