Let a and b be two prime numbers. If seven times a is added to five times b, it gives 129. Find the
value of b.
Answers
Given : a and b be two prime numbers.
seven times a is added to five times b, it gives 129.
To Find : the value of b.
Solution:
a and b be two prime numbers
7a + 5b = 129
5b can end with 5 or 0
if b is odd then 5
if b is even then 0
b can be even if its 2 as its prime number
case 1 : is b is even
then b = 2
=> 7a + 5(2) = 129
=> 7a + 10 = 129
=> 7a = 119
=> a = 17
a= 17 and b = 2 both are prime
and 7a + 5b = 129
case 2 :
if b is odd
then 7a + 5b = 129
7a must end with 4
to end with 4 7 must be multiplied by even number hence a must 2 as 2 is the only even number
7 * 2 + 5b = 129
=> 5b = 115
=> b = 23
b = 23 and b = 2
Value of b = 2 and 23
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