Harriet ran a $1000 \mathrm{~m}$ course in 380 seconds. She ran the first $720 \mathrm{~m}$ of the course at a constant speed of $3 \mathrm{~m} / \mathrm{s}$. She ran the remaining part of the course at a constant speed of $v \mathrm{~m} / \mathrm{s}$. What is the value of $v$ ?
(A) 2
(B) 1.5
(C) 3
(D) 1
(E) 4.5
Since Harriet ran $720 \mathrm{~m}$ at $3 \mathrm{~m} / \mathrm{s}$, then this segment took her $\frac{720 \mathrm{~m}}{3 \mathrm{~m} / \mathrm{s}}=240 \mathrm{~s}$.

In total, Harriet ran $1000 \mathrm{~m}$ in $380 \mathrm{~s}$, so the remaining part of the course was a distance of $1000 \mathrm{~m}-720 \mathrm{~m}=280 \mathrm{~m}$ which she ran in $380 \mathrm{~s}-240 \mathrm{~s}=140 \mathrm{~s}$.

Since she ran this section at a constant speed of $v \mathrm{~m} / \mathrm{s}$, then $\frac{280 \mathrm{~m}}{140 \mathrm{~s}}=v \mathrm{~m} / \mathrm{s}$ which means that $v=2$.

ANSWER: (A)