<PRE><B>Question 352113</B>
A ship using sound-sensing devices above and below water recorded a surface
 explosion 39 seconds sooner on its underwater device than on its above-water
device. 
If sound travels in air at about 1,100 feet per second and in water at about
 5,000 feet per second, how far away was the explosion?
:
let d = distance to the explosion
:
Write a time equation: time = dist/speed
:
{{{d/1100}}} - {{{d/5000}}} = 39
Multiply equation by 55000, to clear the denominators, results
50d - 11d = 55000(39)
39d = 55000(39)
divide both sides by 39
d = 55000 ft
:
:
Check solution by finding the actual times
{{{55000/1100}}} - {{{55000/5000}}} =
50 - 11 = 39</PRE>