Question 8 A log with diameter 60 cm is 3 m in length its hollow centre is 20 cm in diameter.

Find the surface area of the log in cm', including the ends and the inside, correct to one decimal place.

The surface area of the log including the ends and the inside is 80424.8 cm²

Step-by-step explanation:

To determine the surface area of the log with hollow center including the ends and the inside, we will find the surface area of the outer part of the log, surface area of the inner part of the log and the surface area of the two ends; and then sum everything up.

From the question,

Diameter of log = 60 cm

Length of log = 3 m = 300 cm

Diameter of hollow center = 20 cm

For the surface area of the outer part,

Area of the outer part = Circumference of the outer part × length

Circumference = 2πr = πd

∴ Area of the outer part = πd × l

(NOTE: d here is the diameter of the log)

d = 60 cm and l = 300 cm

Area of the outer part = 60π × 300 = 18000π cm²

For the surface area of the inner part,

Area of the inner part = Circumference of the inner part × length = πd × l

(NOTE: d here is the diameter of the hollow center)

d = 20 cm and l = 300 cm

Area of the inner part = 20π × 300 = 6000π cm²

For the surface area of one end

This is the difference between the area of the outer end and the area of the inner end

Here, we can determine the area by using

Area = πr², where r is the radius

Radius = Diameter / 2

Radius of outer end (R) = Diameter of log / 2 = 60cm / 2 = 30cm

Radius of inner end (r) = Diameter of hollow center / 2 = 20cm / 2 = 10 cm

∴ Surface area of one end = πR² - πr² = π(R²-r²)

= π (30²-10²)

= π (900 - 100)

= 800π cm²

This is the area of one end

For the two ends,

Area of the two ends = 2 × 800π cm² = 1600π cm²

Hence, the surface area of the log is 18000π cm² + 6000π cm² + 1600π cm²

Surface area of the log = 25600π cm²

Putting the value of π (π = 3.141592654)

Surface area of the log = 25600 × 3.141592654 cm²

Surface area of the log = 80424.77193 cm²

Surface area of the log = 80424.8 cm²

Hence, the surface area of the log including the ends and the inside is 80424.8 cm² (to one decimal place)

soo this can be solve by using the formula:

f = p( 1 + i)^ n

where f is the future profit

p is the initial profit

i is the percent increase

n is the number of years

a . f = 30000 ( 1.05)^n

b. f = 30000 ( 1.05)^15

f = $62,368