d'anthony borrowed $50,000 today that he must repay in 15 annual endminus−ofminus−year installments of $5,000. what annual interest rate is d'anthony paying on his loan?

Given:
Amount of the loan, PV = $50,000
Number of payment periods, n = 15
Yearly payment, P = $5,000

Let r = annual interest rate.
Then


Insert given information into this equation to obtain
50000r - 5000[1 - (1+r)⁻¹⁵] = 0

Write the equation as
f(r) = 10r + (1+r)⁻¹⁵ - 1 = 0

   --  r     -   f(r)
--------  ----------
0.010   -0.039
0.020  -0.057
0.035  -0.053
0.045  -0.033
0.055  -0.002
0.060   0.017

The solution is obtained graphically (see the accompanying figure) as
r = 0.055 = 5.5%

The annual interest rate is 5.5%

In line with other previous and contemporaneous proposals, in 1912 the meteorologist  alfred wegener  amply described what he called continental drift, expanded in his 1915 book the origin of continents and oceans and the scientific debate started that would end up fifty years later in the theory of plate tectonics.