What is 1+1?

Under what circumstance is 1+1 = 1? I am looking for a word here that can fit into this sentence,

"By_______, 1+1 = 1." Answers shall be revealed in 1 week's time.

Today I went to a workshop in Redhill to get a check on my bike, this workshop is well-known to be reliable among the bikers. I suspected my usual workshop in Tampines is placing me on the chopping board like a Big Fat Carrot after my visit there to get new tires. Apparently they said my brake pads were worn out, especially the rear one and quoted me $32 for a "Denmark' one. I did some research before I went there so i declined upon hearing the high price. So at the Redhill workshop I decided to change the pads anyway since its been more than a year, to my surprise its still in a pretty good condition after I compared it with one the workshop just changed for another guy. Mine still had about 4-5mm of the padding left while the other guy's worn out pad has only about 1mm left. And it only cost me $25, think its a Japanese product so I'm quite fine with it. So while I'm there I decided to get them to check on my squeaky front brake lever. It happened before, I think the start of the year, so the Tampines workshop changed some small part which doesn't seem defective in any way and charged me a whopping $45 for it. Here they said its just some dirt or something and sprayed some lubricants into the lever and its as smooth as ever, no parts dismantled! So I got the uncle to help me tighten my chain a little since I saw him doing for the guy before me and mine looked a little loose. Turns out the tire changing process was pretty f-ed up, realised the locking nuts wasn't tightened, the nut was too tight so the uncle managed to do everything swee swee for me and all I paid was $25 for the brake pad. I even found out that changing engine oil there is cheaper than at Tampines, and since its 'on the way' between NUS and Tampines, they just got a new regular customer.

A word of advice for vehicle owners, be it car or bike or whatever you're driving, try not to change all your brake pads together, because un-seasoned pads are less effective and by changing alternately, you at least have half of them 100% effective.