Two carnot engines A and B are operated in series. The first one A receives heat at `900K` and rejects it to a reservoir at `T K`. The second engine B receives the heat rejected by the first engine and rejects it to a heat reservoir at `400K`. Calculate the value of `T`, when the efficiency ot two engines is the same.

Explanation

To solve the problem of finding the temperature \( T \) at which the efficiencies of two Carnot engines A and B are the same, we can follow these steps:

### Step 1: Understand the Carnot Engine Efficiency Formula
The efficiency \( \eta \) of a Carnot engine is given by the formula:
\[ \eta = 1 - \frac{T_{\text{cold}}}{T_{\text{hot}}} \]
where \( T_{\text{hot}} \) is the temperature at which the engine absorbs heat and \( T_{\text{cold}} \) is the temperature at which it rejects heat.
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