Problem 18

$$\begin{array}{lcl} 18.\: Juliet\:ran\:a\:race\:of\:1000\:m\:in\:4\:laps\:of\:equal\:\\ distance.\:Her\:average\:speeds\:for\:the\:four\:laps\\ were\: 8 \:m, \:8 \:m,\: 6\:m\:and\:5\:m\:per\:second, \:\\respectively.\:What\:was\:her\:average\:speed\:for\:the\\ entire\:race,\:in\:meters\:per\:second\:?\\ \end{array}$$