Given three automates that deal with the cards with the pairs of natural numbers. The first, having got the card with ($a,b)$, produces new card with $(a+1,b+1)$, the second, having got the card with $(a,b)$, produces new card with $(a/2,b/2)$, if both $a$ and $b$ are even and nothing in the opposite case; the third, having got the pair of cards with $(a,b)$ and $(b,c)$ produces new card with $(a,c)$. All the automates return the initial cards also. Suppose there was $(5,19)$ card initially. Is it possible to obtain 
a) $(1,50)$? 
b) $(1,100)$? 
c) Suppose there was $(a,b)$ card initially $(a<b)$. We want to obtain $(1,n)$ card. For what $n$ is it possible?
To solve this problem, we need to analyze the operations performed by the automates and determine if we can transform the initial card \((5, 19)\) into the desired cards \((1, 50)\) and \((1, 100)\). We will also generalize the solution for any \(n\).

1. **Understanding the operations:**
   - **First automate:** Given \((a, b)\), it produces \((a+1, b+1)\).
   - **Second automate:** Given \((a, b)\), it produces \((a/2, b/2)\) if both \(a\) and \(b\) are even.
   - **Third automate:** Given \((a, b)\) and \((b, c)\), it produces \((a, c)\).

2. **Preservation of differences:**
   - The first automate preserves the difference \(a - b\) because \((a+1) - (b+1) = a - b\).
   - The second automate also preserves the difference \(a - b\) when both \(a\) and \(b\) are even because \(\frac{a}{2} - \frac{b}{2} = \frac{a - b}{2}\).
   - The third automate, given pairs \((a, b)\) and \((b, c)\), produces \((a, c)\). If \(a - b\) and \(b - c\) are divisible by an odd natural number \(q\), then \(a - c\) is also divisible by \(q\).

3. **Initial card \((5, 19)\):**
   - The difference \(5 - 19 = -14\).
   - The odd divisors of \(-14\) are \(1\) and \(7\).

4. **Part (b): Is it possible to obtain \((1, 100)\)?**
   - The difference \(1 - 100 = -99\).
   - The odd divisors of \(-99\) are \(1\), \(3\), \(9\), and \(11\).
   - Since \(7\) is not a divisor of \(-99\), it is impossible to transform \((5, 19)\) into \((1, 100)\).

5. **Part (a): Is it possible to obtain \((1, 50)\)?**
   - The difference \(1 - 50 = -49\).
   - The odd divisors of \(-49\) are \(1\) and \(7\).
   - Since \(7\) is a divisor of \(-49\), it is possible to transform \((5, 19)\) into \((1, 50)\).

6. **General case: Given \((a, b)\) with \(a < b\), for what \(n\) is it possible to obtain \((1, n)\)?**
   - The difference \(a - b\) is preserved modulo any odd divisor \(q\).
   - To obtain \((1, n)\), the difference \(1 - n\) must share at least one odd divisor with \(a - b\).
   - Therefore, \(n\) must be such that \(1 - n\) shares an odd divisor with \(a - b\).

- Part (a): True. The final answer is \( \boxed{ (1, 50) } \).