A particle would take a time t1 to move down a straight tunnel from the surface of earth to its centre. If g is assumed to be constant, time would be t2. Find t1/t2.

in this problem, to calculate the relation between times, use the concept given on page 8 case ii......, you will get gravity value as a function of distance from the surface.....relate it with time.
in second case, calculate time by assuming gravity
g’/g = x/(x2+R2)3/2 / R ...relate it with time.
Do try and tell me....