Answer
Hot bodies radiate heat. Bodies can also receive heat through radiation. When alone, a penguin radiates heat into the surroundings.
Each penguin radiates a certain amount of heat. In the huddle, some other penguin will receive it, as only a little of it is radiated into the surroundings. The mentioned penguin will also receive a portion of someone else's radiated heat. As a result, bodies are warmer when in a huddle than when they are on their own.
Work Step by Step
Given above.