Question

What is the rate at which reciprocal of a number changes with respect to the number if the number is equal to 7? Let n be the number and r be the reciprocal of the number?

Answer 1

r = 1/n
dr/dt = -n^2 dn/dt
when n = 7, r = 1/7

dr/dt = -49 dn/dt

we have missing information

Answer 2

r = 1/n
dr/dn = -1/n^2
...