How can I distribute a random number of faults over 12 months in excel 2010?

Row\Col	B	C	D	E	F	G
2	Failures		Scale
3	9		12.884
4
5	Failure	Time	Norm		Month	Failures
6	1	2.084	1.941		1	0
7	2	2.430	2.263		2	1
8	3	5.022	4.677		3	1
9	4	5.334	4.968		4	0
10	5	5.539	5.159		5	2
11	6	6.250	5.822		6	2
12	7	7.217	6.722		7	1
13	8	10.598	9.871		8	0
14	9	12.698	11.827		9	0
15	10	12.885	12.001		10	1
16	11	13.914	12.959		11	0
17	12	14.279	13.299		12	1
18	13	15.024	13.993		Total	9
19	14	15.300	14.250
20	15	17.834	16.610
21	16	18.081	16.840
22	17	19.148	17.834
23	18	20.146	18.764
24	19	20.314	18.920
25	20	22.509	20.965
26	21	26.216	24.418
27	22	26.295	24.491
28	23	29.085	27.090
29	24	31.333	29.183
30	25	33.902	31.576

The only input on the sheet is B3, the number of failures in a 12-month period.

Col C generates random failure events with an exponential distribution based on the number of failures over 12 months, N. Col D scales those times such that the (N+1)th failure occurs just beyond the 12-month window. Col G is a histogram of the failure times in col D.

The workbook is at https://app.box.com/s/ug9yvk0472laaga4i7lv

You're welcome.