Finding the Origin Time of earthquakes?

Normally the origin time and the distances are calculated by the use of arrival time of both P wave and S wave. The speed varies according the density of the medium through which it passes. But the speed ratio is 1.7:1.The speed difference is about 8 K/M per second arrival time difference. Learn about the characters of waves.

Mainly there are 4 types of waves generated by earthquakes.1. Primary wave or compression wave. The speed of this wave will be in the order of 13 to 17 km per second the fastest of all waves.This wave will travel through all mediums like solids, semisolids and liquids. This will make the particles of the earth to expand and compress .The strength of this wave will be about one tenth of secondary wave. Therefore we may not feel it. Somebody may feel giddiness. Only the instruments will sense these waves. It will move the particles in the direction of its propagation.. 2. Secondary wave travels about half of the speed of primary wave. The correct ratio is 1.7 :1 This causes the earth to move in perpendicular to the direction of its propagation. The shaking will be felt by human. This wave will not travel through liquids. This is also called body waves.The above 2 waves are generated from the point called focus. That is the point where the earthquake starts. Therefore these waves are called body waves.3. Love wave the name of the person found the wave. This is generated at the surface of the earth due to reflection and refraction of the body waves. This will generate only lateral movements. This will cause the waters to move in sideways. The water in small tanks and ponds will spill out and will become muddy.4. Rayleigh wave most dangerous of all .These waves comes at last which generates rolling movement of the earth. These two waves are called surface waves.The shaking during earthquake will be about 1mm to 70 mm for ordinary earthquakes and it may go up to 240 mm in extraordinary cases.The Richter scale 3 will shake the earth for 0.1 mm if it is measured at a distance of 100 km from epicenter. This shaking will increase by ten fold for each Richter scale and reduce by inverse square of distance.

Since P waves travel at anywhere from 5-8 km/s depending on the composition of the soil the question can not be answered with the information provided. I suspect the neccesary information is somewhere in your question in the book. the general form would be

5:10 - T seconds

T = 4800/S where S is the speed of the p wave