The book fair has 390 books. they have 5 more boxes with 10 books in each box. count by tens how many books are at the book fair

The current no. of books at the book fair is 390. With 5 more boxes, each with 10 books, we will have to add that many number of books to 390.

5 boxes each with 10 books = 5 x 10 = 50

current number of books = 390

total number of books = 390 + 50 = 440

There are 440 books at the book fair.

*I am unsure of what you mean by "count by tens", but if your teacher is asking you how many "ten books" are in the book fair, then there would be 44 sets of 10 books.

i found two solutions,   n = 2 • ± √3 = ± 3.4641

step-by-step explanation:

step-by-step explanation:

12: 00 p.m. to 7: 00 p.m. is a total of 7 hours.

4: 00 p.m. to 7: 00 p.m. is a total of 3 hours.

this means that from 4: 00 p.m to 7: 00 p.m. this represents 3/7 of what was lost from 12: 00 p.m. to 7: 00 p.m.

after knowing this, after doing 11,600 - 6,800 = 4,800

4,800 represents 3/7 of what was lost for 7 hours.

we then divide 4,800 by 3 which gets 1,600.

because we know that 1,600 represents 1/7 of how much water was lost, we just have to multiply by 7, which gets 11,200.   after adding 11,200 to how much water was left at 7: 00 p.m. which was 6,800. 11,200 + 6,800 = 18,000

this means that the pool originally had 18,000 gallons in the pool.

you can also check your work by doing 18,000 - 4(1600), which becomes           1800 - 6400 which gets you 11,600.