Answer :
400 + (n-1) (-5) = 322 + (n-1) (-3)
-5n + 5 = 322
-3n + 3 | 405 - 5n
=325 - 3n
80=2n
n=40 n - 1 = 39
Answer = 39 , 39 weeks until they weigh the same
-5n + 5 = 322
-3n + 3 | 405 - 5n
=325 - 3n
80=2n
n=40 n - 1 = 39
Answer = 39 , 39 weeks until they weigh the same