Number of shelves in a music store = 58.

Number of CDs in each shelf = 42.

Round up 58 to 60 and round down 42 to 40.

Total number of CDs in the music store = number of shelves × number of CDs in each shelf

= 60 × 40 = 2400

Therefore, total estimated number of CDs in the store is 2,400.

Number of postcards that Sean bought from Canada = Total number of postcards - Number of postcards from Sweden and Hungary

= 768 - 342

= 770 - 340 = 430

The number of postcards bought from Canada rounded to the nearest ten, is 430.

Round 12 down to 10 and 9 up to 10.

Time taken = 10 × 10 = 100

So, estimated time taken to decorate a vase 9 times is 100 minutes.

Round 19 to 20 and 9 to 10.

Time taken by Robert to prepare 9 flower beds is about "20 × 10 = 200" minutes.

Round 12 to 10 and 47 to 50.

Total number of students in the school = 10 × 50 = 500.

Frank traveled 576 and 326 miles on two consecutive days.

Frank traveled a total distance of 910 miles on the two days together.

Amount the museum collected on that day = Average price of the ticket × Number of people who visited the museum.

= $29 × 543.

$29 can be rounded to $30.

543 can be rounded to 540.

So, $30 × 540 = $16,200.

So, $16,200 is the correct answer.

An estimate is enough to find the number of groups that can be made with 59 students.

Number of students in each group = 5

Total number of students in the class = 59

59 can be rounded to 60.

Number of groups that can be made with the given number of students = Total number of students rounded to nearest ten ÷ Number of students in each group

= 60 ÷ 5 = 12

Therefore, the estimated number of groups that can be formed is 12.

Round 17 up to 20 and 12 down to 10.

Number of pencils = 20 × 10

So, Wilson bought about 200 pencils.

Round up 289 to the nearest hundred = 300

Round down 120 to the nearest hundred = 100

300 + 100 = 400

So, the estimated number of letters written are about 400.

Amy has collected 831 marbles.

Round down 831 to 800.

She wants to collect 1,000 marbles.

So, the number of marbles she needs to collect = 1,000 - 800 = 200.

John wants to pack 5 oranges in each box and he has 38 oranges.

38 can be rounded to 40.

Number of boxes required = Estimated number of oranges ÷ Number of oranges in each box.

= 40 ÷ 5 = 8

Therefore, John needs about 8 boxes to pack all the oranges.

Ursula wants to use 4 roses in each bouquet and she has 77 roses.

77 can be rounded to 80.

Number of bouquets = Estimated number of roses ÷ Number of roses in each bouquet.

= 80 ÷ 4 = 20

Therefore, Ursula can make about 20 bouquets by using 77 roses.

Number of points for each round = 33

33 points can be rounded as 30 points.

Number of rounds played = 9

Number of rounds won by Paula = 6

Points earned by Paula at the end of the game = Number of points earned by Paula in each round × Number of rounds she won

= 30 × 6

= 180

Therefore, Paula earned 180 points in the game.

Cost of an item = $29

Cost of 48 items = 29 × 48

= 30 × 50

= $1500