I was doing the laundry and then it happened

No idea but you're on a roll. Might want to invest in that lottery ticket today.

1/22 * 50/2000

1/22* 1/40 = 1/880 has considerable merit as an answer.

However, consider this

When I use the fabric softener from now on, the number of washes until the end of the bottle will be:

40 80 120 160 200 240 280 320 360 400 440

ie 440 washes from exactly 11 bottles

When I use the laundry powder from now on, the number of washes until the


end of the box will be:

22 44 66 88 110 132 154 176 198 220
242 264 286 308 330 352 374 396 418 440

ie exactly 440 washes from 20 boxes

The probability of it happening again is 1/440.

If I had started from a box with 1 portion already used then 22n +21
would never co-incide with a bottle multiple of 40.

Which is why Jespah and I will share the winnings in the unlikely event that I ever buy a lottery ticket.