Question

for a right circular cone, if the radius is reduced to1/5 its original size and the slant height is reduced to 1/6 its original size, find the surface area if the original radius is 8 centimeters and the original slant height is 13 centimeters.

Answer 1

Is it 18.93?

Answer 2

No

slant area = pi *r *l

original r = 8 but this is reduces to 1/5 ot the original
original l = 13 but this is reduced to 1/6 of teh original

so work out the new r and l then calculate
pi*r*l

Answer 3

hint:
using data from the text of the problem, we can write that the new area \(S'\), is a function of the original area \(S\), namely the area computed from the non-reduced, or original dimensions, so we have:
\[S' = \pi r'h' = \pi \cdot \frac{r}{5} \cdot \frac{h}{6} = \frac{{\pi rh}}{{30}} = \frac{S}{{30}}\]

Answer 4

Working on it! :)

Answer 5

Both methods are identical

One converts the dimensions before calculating the area
The other converts the area after calcularting original

pi * r * l

is all you need for this

Answer 6

But that would make it 326.56 and that wouldn't be the answer..

Answer 7

Oh, sorry, forgot the reduction part. :P Never mind.

Answer 8

hint:
please compute this:
\(S=\pi \times 8 \times 13=...?\)

Answer 9

Yes, that's326.56. Just trying to convert the 8 and 13.

Answer 10

Would it be 18.84?

Answer 11

No

Answer 12

As has been shown above:

take the ORIGINAL area pi * r * l and divide by 30

Answer 13

Ah, 18.63

Answer 14

No - I don't think that is correct either

show me pi *r * l with original values

Answer 15

Ah, so it's 18.74.

Answer 16

You agree @MrNood ?

Answer 17

no

please show how you worked this out

step by step

Answer 18

OK wait - I may be mistaken

I read it as asking for the slant area - but it asks for the 'surface area'

My mistake - wait a moment

the formula is
A = pi*r *l + p*r^2
= pi * r (r+l)

Answer 19

18.93 is correct

I apologise for your wasted time....