A body takes $4\, {min}$. to cool from $61^{\circ} {C}$ to $59^{\circ} {C}$. If the temperature of the surroundings is $30^{\circ} {C}$, the time taken by the body to cool from $51^{\circ} {C}$ to $49^{\circ} {C}$ is $....\,min$
JEE MAIN 2021, Medium
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$\frac{\Delta T }{\Delta t }= K \left( T _{ t }- T _{ s }\right)$
$\frac{61-59}{4}= K \left(\frac{61+59}{2}-30\right)$
$\frac{51-49}{ t }= K \left(\frac{51+49}{2}-30\right)$
$\frac{ t }{4}=\frac{60-30}{50-30}=\frac{30}{20}$
$t =6$ minutes
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