A problem by Raiyun Razeen
Level
pending
A, B, C and D are four brothers. Two of them are twins. Each of their ages is prime number. Sum of their ages is 23. What is the sum of the ages of twin brothers?
The answer is 10.
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1 solution
Every prime number except 2 is odd. The sum of four odd numbers can not be odd, so one of the ages is 2, and the sum of the age of other brothers is 23 - 2 = 21. If we assume that the age of one of the twin brothers is x years old, the other ones age must be 21 - 2x which should be a prime number. Through trial and error, we find that x = 5. So the sum of their age is 5 + 5 =10.