You get $4 today and repay $5 when you get your paycheck in one week to Friendly's. What's the effective annual return Friendly's earns on this lending business? If you were brave enough to ask, what APR would Friendly's say you were paying?

This will be the ultimate result in one year's time.

WEEKS

1 4.00 5.00
2 5.00 6.25
3 6.25 7.81
4 7.81 9.77
5 9.77 12.21
6 12.21 15.26
7 15.26 19.07
8 19.07 23.84
9 23.84 29.80
10 29.80 37.25
11 37.25 46.57
12 46.57 58.21
13 58.21 72.76
14 72.76 90.95
15 90.95 113.69
16 113.69 142.11
17 142.11 177.64
18 177.64 222.04
19 222.04 277.56
20 277.56 346.94
21 346.94 433.68
22 433.68 542.10
23 542.10 677.63
24 677.63 847.03
25 847.03 1,058.79
26 1,058.79 1,323.49
27 1,323.49 1,654.36
28 1,654.36 2,067.95
29 2,067.95 2,584.94
30 2,584.94 3,231.17
31 3,231.17 4,038.97
32 4,038.97 5,048.71
33 5,048.71 6,310.89
34 6,310.89 7,888.61
35 7,888.61 9,860.76
36 9,860.76 12,325.95
37 12,325.95 15,407.44
38 15,407.44 19,259.30
39 19,259.30 24,074.12
40 24,074.12 30,092.66
41 30,092.66 37,615.82
42 37,615.82 47,019.77
43 47,019.77 58,774.72
44 58,774.72 73,468.40
45 73,468.40 91,835.50
46 91,835.50 114,794.37
47 114,794.37 143,492.96
48 143,492.96 179,366.20
49 179,366.20 224,207.75
50 224,207.75 280,259.69
51 280,259.69 350,324.62
52 350,324.62 437,905.77

DISGUSTING.
They would probably say it is 25% weekly.