What is the meaning of 'Wouldn’t you know?'

Question

The passage below comes from Emily's runaway imagination by Beverly Cleary.

During the week the stationmaster at the depot telephoned Mama to say that a crate of books had arrived from the state library. Mama had Grandpa pick up the crate in his Ford and deliver it to the Commercial Clubrooms. And wouldn’t you know?

That was the week the tomatoes were ripe and Mama was so busy canning tomatoes and selling tomatoes to other ladies who wanted to can them that she did not have time to go uptown and open that crate.

Could you explain to me the meaning of 'wouldn’t you know'? And if you don't mind, give me another example of this phrase with common words but with difficult nuance to me.

Answer 1

Wouldn't you know is an idiomatic phrase. It's synonymous with:

You wouldn't believe it

Phrase(idiomatic)

Expresses dismay or annoyance, especially at bad luck or misfortune. Wouldn't you know it! I left my wallet at home.

(www.yourdictionary.com)

The narrator is expressing disbelief at the seemingly unlucky coincidence related in the second paragraph, that meant mama was unable to go and open the crate:

That was the week the tomatoes were ripe and Mama was so busy canning tomatoes and selling tomatoes to other ladies who wanted to can them that she did not have time to go uptown and open that crate.

Another example of usage, (this time not related to misfortune):

I was perusing English Language and Usage today, wouldn't you know it? I learned more about words and their usage than I did in 2 years at school.

Answer 2

"Wouldn't you know" is used to express something which is not surprising or unexpected, but at the same time a little annoying and frustrating.

For example, I was running late to office and, wouldn't you know, my bike got a flat tire.

You may check out the following dictionary links:

Merriam-Webster

Longman