Tóm tắt:
\(v=36\left(\dfrac{km}{h}\right)\)
\(t=30p'=\dfrac{1}{2}h\)
\(s'=6000m=6km\)
\(v'=30\left(\dfrac{km}{h}\right)\)
\(t''=20p'=\dfrac{1}{3}h\)
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a, \(s=?\left(m\right)\)
b, \(s''=?\left(m\right)\)
Giải:
a, Quãng đường đầu tiên là:
\(s=v.t=36.\dfrac{1}{2}=18\left(m\right)\)
b, Quãng đường thứ ba là:
\(v_{tb}=\dfrac{s}{t}=\dfrac{18+6+s''}{\dfrac{1}{2}+\dfrac{1}{5}+\dfrac{1}{3}}=\dfrac{24+s''}{\dfrac{15+6+10}{30}}=\dfrac{24+s''}{\dfrac{31}{30}}=\dfrac{30\left(24+s''\right)}{31}\)
\(\Leftrightarrow30=\)\(\dfrac{30\left(24+s''\right)}{31}\)
\(\Leftrightarrow30.31=30.\left(24+s''\right)\)
\(\Leftrightarrow31=24+s''\)
\(\Leftrightarrow s''=7\left(km\right)\)
Vậy.....................................................