a, b, c are prime numbers that satisfy: a > b > c a + b + c = 5 2 a − b − c = 2 2 What is the value of a b c ?
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37+13+2=52 37-13-2=22 now 37 13 2=962
(a+b+c) - (a-b-c) = 52-22 ---> 2b + 2c = 30 --> 2(b+c) = 30 ----> b+c = 15 ----> (a+b+c) - (b+c) = 52 - 15 ---> a= 37. Because b and c are prime numbers so 15 = 13 + 2 ---> b>c so b= 13 and c = 2 . Thus abc = 37.13.2 = 962
a+(b+c)=52 a-(b+c)=22 a=37 b+c=15 hence b=13 and c=2
You can shorten your prime number search by realizing that a − ( 5 2 − a ) = 2 2 . By starting at 4 7 and working down the primes, you quickly realize that a = 3 7 , and thus b = 1 3 and c = 2 .
3 7 × 1 3 × 2 = 9 6 2
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Summing the two equations: 2 a = 7 3 a = 3 7
Therefore, b + c = 1 5 .
The sum of an odd number and an even number is odd: one of b and c must be odd and the other even.
There is only one even prime: 2 (which is also the smallest). Therefore, c = 2 .
From that, b = 1 3 .
Finally, a b c = 3 7 × 1 3 × 2 = 9 6 2