A principal of $2,000 was invested in a savings account for 4 years. If the interest earned for the period was $240, what was the interest rate?

A = P (1+r%) ⁿ, where P = initial capital, r% = interest and n = number of years

After 4 years she earned $240, so the new capital = $2240

2240 = 2000 (1+r) ⁴

2240/2000 = (1+r) ⁴

1.12 = (1+r) ⁴

ln (1.12) = ln (1+r) ⁴

ln (1.12) = 4ln (1+r)

0.1133286 = 4ln (1+r)

0.02833 = ln (1+r)

(1+r%) = e⁰.⁰²⁸³³

r = e⁰.⁰²⁸³³ - 1

r = 1.028737 - 1

r = 0.0287

or in % → r = 2.87%