math help please?

Question

6: Find the surface area of a baseball with diameter 3 inches.
113.04 sq. in
77.9 sq. in
45.32 sq. in
28.26 sq. in
20: Paraffin comes in blocks 3" X 5" and 1/2 " thick, 4 blocks in a package. It is melted and poured as a seal into the top of cylindrical jelly jars 2 1/2 inches in diameter, to a depth of 1/4 inch. How many jars can be sealed with one package of paraffin?
15.5
24
36
45.5


21: Find the cost of 500 pieces of lumber, 2" X 8", 18' at $180 per 1000 board feet. (See assignment 7.3 for the proper formula for board feet.)
$2160
$2500
$2230
$1980

Answer 1

Surface area for a sphere formula

s = 4 π r²

s = 4(3.141592654(1.5)²

s = 4(3.141592654(2.25)

s = 12.56637061(2.25)

s = 28.17433388

- - - - - -s-

Answer 2

6. Formula: SAsphere= (4)(pi)(r^2)
d=2r, so r=3/2 or 1.5 inches
SA= (4)(3.14)(1.5)(1.5) = 28.26 sq in.

20. You divide the total volume of the 4 paraffin blocks by the volume of one wax seal.
Vblock = (3)(5)(.5)(4) <-- 4 blocks = 30 cu in.

Vseal = (pi)(r^2)(h) = (3.14)(1.25)(1.25)<-- [1.25 is the radius, or 2.5/2] (.25)= 1.2265625 cu in.

#seals = 30/1.2265625 = about 24

21. steps: a. find out how many board feet there are.
(Thickness x Width x Length) / 144 = Board Feet
(2)(8)(18 times 12 to get inches)/144 = 24 bf
b. set up this proportion: $180/1000bf = $/24
price per piece of lumber is [(180)(24)]/1000 = 4.32
c. multiply this by 500 = $2160

Answer 3

#6:
Surface area of a sphere is
4(pi)(r^2)

Remember that radius (r) is half the diameter, so use 1.5 for the radius in this case.
------------

You asked #20 and #21 last week.

#20 - calculate the volume of a block then multiply by the number of blocks in a package to get the total volume of parafin.
The seal on the top of the jar is a cylinder (using the diameter and depth=height listed).
Finally take the volume of the parafin divided by the volume of the seal to get how many jars.

#21 - I don't know how to do board feet, so you'll have to go back to that assignment it references.