If a group is of order $20$. Its factorisation is $2^2*5$. So, there are subgroups of order $2,4$ and $5$. Whether a $2$-Sylow subgroup means subgroup of order $2$ or $4$ ($2^2$) ??
From Sylow's third theorem i can say there is a normal subgroup of order $5$ ($1+5k|20$) and number of $2$-sylow subgroups are ($1+2k|20$) = $2$ . So there are $2$ subgroups order $4$. Correct me, if i am wrong.