To solve this problem, let's start by determining the speed Jack drives from A to B.
Let the distance from A to B be \(d\) and let his original speed be \(v\).
From the information given, we know that:
\[ \text{Time} = \text{Distance} / \text{Speed} \]
Thus, for the journey from A to B:
\[ 2 \text{ hours} = \frac{d}{v} \]
From this, we can express the distance \(d\) in terms of speed \(v\):
\[ d = 2v \]
Now, Jack increases his speed by 25% for the return journey. His new speed \(v_{\text{new}}\) will be:
\[ v_{\text{new}} = v + 0.25v = 1.25v \]
Now we can find the time taken for the return journey from B to A using the new speed \(v_{\text{new}}\):
\[ \text{Time for return journey} = \frac{d}{v_{\text{new}}} \]
Substituting the expressions we've established:
\[ \text{Time for return journey} = \frac{d}{1.25v} \]
Substituting \(d = 2v\):
\[ \text{Time for return journey} = \frac{2v}{1.25v} \]
The \(v\) terms cancel out:
\[ \text{Time for return journey} = \frac{2}{1.25} \]
Calculating \( \frac{2}{1.25} \):
\[ \text{Time for return journey} = \frac{2 \times 100}{1.25 \times 100} = \frac{200}{125} = \frac{8}{5} = 1.6 \text{ hours} \]
Thus, the time Jack will take for the return journey is:
\[ \boxed{1.6} \text{ hours} \text{ (or 1 hour and 36 minutes).} \]
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