1) A cyclist traveling at a constant speed of $5 \mathrm{~m} / \mathrm{s}$, how many kilometers does he travel in 3 hours?
(A) $15 \mathrm{~km}$
(B) $18 \mathrm{~km}$
(C) $50 \mathrm{~km}$
(D) $54 \mathrm{~km}$
(E) none of the above.
1) The answer is $(\mathbf{D})$.

There are 3600 seconds in an hour, so in 3 hours the cyclist travels $5 \cdot 3 \cdot 3600 \mathrm{~m}$, which is $54 \mathrm{~km}$.