Speed of boat in still water is 13 miles per hour and speed of current is 4 miles per hour
<h3><u><em>Solution:</em></u></h3>
Let s = the speed of the boat in still water in miles/hour
Let c = the speed of the current in miles/hour
<em><u>Formula to remember:</u></em>
If the speed of a boat in still water is s miles/hr and the speed of the current is c miles/hr, then:
Speed downstream = (s + c) miles per hour
Speed upstream = (s - c) miles per hour
<em><u>Given:</u></em>
boat traveled 153 miles downstream and back
distance for downstream = 153 miles
distance for upstream = 153 miles
time taken for downstream = 9 hours
Time taken for upstream = 17 hours
<em><u>The relation between speed, distance and time is given as:</u></em>
<em><u>For downstream:</u></em>
s + c = 17 ------- eqn 1
<em><u>For upstream:</u></em>
s - c = 9 ------- eqn 2
<em><u>Let us solve eqn 1 and eqn 2 to find values of "s" and "c"</u></em>
Add eqn 1 and eqn 2
s + c = 17
s - c = 9
(+) -------------
2s = 26
<h3>s = 13</h3>
Substitute s = 13 in eqn 1
13 + c = 17
c = 17 - 13 = 4
<h3>c = 4</h3>
Thus the speed of boat in still water is 13 miles per hour and speed of current is 4 miles per hour