Problema Solution
The number of long distance phone calls between two cities in a certain time period varies jointly as the populations of the cities,p^1and p^2, and inversely as the distance between them.If 90,000 phone calls are made between two cities 550 miles apart with populations of 120,000 and 70,000, how many calls are made between cities with populations of 60,000 and 55,000 that are 250 miles apart?
Answer provided by our tutors
let 'x' be the number of calls between 2 cities with populations p1 and p2 and distance 'd' between them
x = k*(p1+p2)/d, where k is constant
90,000 phone calls are made between two cities 550 miles apart with populations of 120,000 and 70,000
90000 = k*(120000 + 70000)/550 => k = 90000*550/190000
k = 9*55/19
for cities with populations of 60,000 and 55,000 that are 250 miles apart we have
x = (9*55/19)*(60000 + 55000)/250
x = 11,984 calls