wrong grammar

while i was helping robin with his math assignment i encountered the following in a book:

It costed P 7.00 to develop each picture.

what the ... ?!?!?

"costed"?!?!?!

wrong grammar! "costed"?!?!

duh. i can probably let this pass if it was on the internet where words change in less than a second but this thing is in a published book. its printed on paper.

lousy editing.

okay. the sentence should read:

It cost P 7.00 to develop each picture.

that is the grammatically correct way. and i told robin that fact. the book is wrong.

the book i am referring to is:

discovering math for global learners (4)
published & distributed by rex book store
page 136