The Puzzle: RE + MI = FA. DO + SI = MI. LA + SI = SOL. (Replace letters with digits and have the sums be true.)
Some countries use do re mi fa sol la ti do, and some countries use alphabet letters instead. So, what is the difference between Do Re Me and A B C really? And which one is best to learn from? I'll give you my opinion in this brief article:

In Hindustani (North Indian) classical music, an octave is called saptak and has seven notes called swara. These notes are sa, re, ga, ma, pa, dha, ni (similar to the Western do re mi fa so la ti). The first and fifth notes (sa and pa) have only one variant. The other five notes (re, ga, ma, dha, and ni) have two variants each.

G is do. A is re. B is mi. C is fa. D is sol. E is la. F# is ti. G is do. Here you are with the sol-fa notes to the hymn Amazing Grace: A (sol) ma (do) zing (mi) grace (mi)! How (re) sweet (do) the (la) sound (sol) That (sol) saved (do) a (mi) wretch (mi) like (re) me (sol)! I (mi) once (sol) was (mi) lost (mi), but (re) now (do) am (la) found
Musical notes using syllables: Do, Re, Mi, Fa, Sol, La and Ti. The names of musical notes can also be represented using syllables, as Do, Re, Mi, Fa, Sol, La and Ti. Some languages use Si instead of Ti. These musical note names match the C major scale, the one we sang before. That means that: Do is C; Re is D; Mi is E; Fa is F; Sol is G; La is Moda na taniec z lat 60. wraca, więc pora nadrobić zaległości. Gama solmizacyjna to podstawa każdej lekcji muzyki. Proste "Do-re-mi-fa-sol-la-si-do" śpiewał każdy z nas, mało kto jednak wie, czemu do poznawania skali dźwięków używa się właśnie tych sylab. Po odpowiedź należało się cofnąć aż do XI w. . 162 309 306 376 431 171 445 50

do re mi fa so la ti do in letters