if i have a cylinder with a radius of 5, and a height of 8, what is its surface area.

this year, beavis is 4 times as old as Mavis, while in 5 years time, he will be 3 times as old as mavis. what are the current ages of beavis and mavis.

p.s. i already found the answer (beavis is 40, and Mavis is 10), but i am not really sure how to work it out and what steps to take. could you please write a solution for me.

B=4M                          (1)

B+5=3(M+5)               (2)

Sub (1) into (2)

4M+5=3(M+5)

4M+5=3M+15

M=10                        Marvis is 10

B=4*10=40                Beavis is 40

If you don't understand make sure you ask for more explaniation.

NEXT time is it better to put your new question up in a new post    

Cylinder:   r = 5     ;   h = 8

O=2*pi*r*(r+h)  = $${\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{\pi}}{\mathtt{\,\times\,}}{\mathtt{5}}{\mathtt{\,\times\,}}\left({\mathtt{5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{8}}\right) = {\mathtt{408.407\: \!044\: \!966\: \!673\: \!121}}$$

408.41  is right !

if i have a cylinder with a radius of 5, and a height of 8, what is its surface area. p.s. i have already worked out the answer, but my teacher and i are having a debate on what the answer was. my answer was 408.41, and hers was 408.2. Which one is right ?

$$\small{\text{$ \begin{array}{rcl} \mathrm{radius~}r=5\\ \mathrm{height~}h=8 \\\\ \hline \\ \mathrm{surface~area~} O&=&\pi r^2+ \pi r^2 + 2\pi r*h \\ O&=&2\pi r ( r + h ) \\ O&=&2\pi 5 ( 5 + 8 ) \\ O&=&2\pi 5 \cdot 13 \\ O&=&2\cdot 5 \cdot 13 \pi \\ O&=&130 \pi \\ \end{array} $}}$$

If you set $$\small{\text{$\pi=3.14$}}$$  you get $$\small{\text{$ O=130\cdot 3.14 = 408.2 $}}$$

But if you set $$\small{\text{$\pi=3.14159265359$}}$$   you get the better answer $$\small{\text{$ O=130\cdot 3.14159265359 = 408.407044967 $}}$$

this year, beavis is 4 times as old as Mavis, while in 5 years time, he will be 3 times as old as mavis. what are the current ages of beavis and mavis.

p.s. i already found the answer (beavis is 40, and Mavis is 10), but i am not really sure how to work it out and what steps to take. could you please write a solution for me.