Namba ya mteja na tarehe ya bili ni sahihi.

Here ya is the associative/genitive marker. It often corresponds to English of or the possessive idea in phrases like customer number and bill date.

So:

• namba ya mteja = literally number of customer
• tarehe ya bili = literally date of bill

Swahili usually builds these noun combinations with noun + associative marker + noun.

Because there are two separate possessive-style noun phrases:

1. namba ya mteja
2. tarehe ya bili

Each phrase needs its own linker. In English, we can say customer number and bill date, but in Swahili each relationship is shown explicitly.

So the structure is:

• [namba ya mteja] na [tarehe ya bili] ni sahihi

Ya agrees with the first noun in each phrase, not the second one.

So:

• in namba ya mteja, ya agrees with namba
• in tarehe ya bili, ya agrees with tarehe

Both namba and tarehe take the associative form ya, so the phrases look parallel.

If the first noun belonged to a different noun class, the linker would change. For example:

• kitabu cha mteja = the customer’s book
• wateja wa kampuni = the company’s customers

So the form of the linker depends on the noun being described.

Here na means and. It joins the two noun phrases:

• namba ya mteja
• tarehe ya bili

So the subject of the sentence is a compound subject: the customer number and the bill date.

Swahili na can also mean with in other contexts, but here it clearly means and.

Because ni is an invariable copula in this kind of sentence. It does not change for singular or plural.

So:

• Namba ... ni sahihi = The number is correct
• Namba ... na tarehe ... ni sahihi = The number and the date are correct

Unlike English is/are, Swahili ni stays the same.

Sahihi means correct, right, or accurate. In this sentence it works as the predicate description after ni.

So:

• ni sahihi = is/are correct

A useful thing to notice is that sahihi does not change form here. Many common descriptive words in Swahili, especially borrowed ones, can stay unchanged in this kind of predicate use.

Because Swahili usually puts the main noun first, followed by the possessor or related noun.

So the pattern is:

• namba ya mteja = number of the customer
• tarehe ya bili = date of the bill

English often uses a noun directly before another noun, as in customer number or bill date, but Swahili normally uses this noun + ya/wa/cha... + noun structure instead.

Swahili does not have articles like English a, an, and the.

Whether something is understood as a customer number, the customer number, or just customer number depends on context.

So Namba ya mteja na tarehe ya bili ni sahihi can naturally be translated with the in English if the context makes them specific.

They are common Swahili words, but they are borrowed historically:

• namba = from number
• bili = from bill
• tarehe = from Arabic origin

This is very normal in Swahili. Many everyday words come from Arabic, English, and other languages, but they are fully natural parts of modern Swahili vocabulary.

It normally means that both are correct:

• the customer number is correct
• the bill date is correct

English and Swahili both allow this kind of coordinated subject with one predicate. So ni sahihi applies to the whole combined subject.