Using, $\theta=\omega_{0} t+\frac{1}{2} \alpha t^{2}$
$\therefore 2 \pi \times 10=0+\frac{1}{2} \alpha \times 3^{2}=\frac{9}{2} \alpha \ldots(i)$
For the rotation of fan in next three second, the total time of revolutions
$=$$3+3=6 s$
Let total number of revolutions $=N$
Then angle of revolutions, $\theta^{\prime}=2 \pi \mathrm{N}$ rad
$\therefore 2 \pi N=0+\frac{1}{2} \alpha \times 6^{2}=18 \alpha$ $...(ii)$
Dividing $(ii)$ by $(i),$ we get
$N=40$
No. of revolutions in last three seconds
$=40-10=30$ revolutions
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