The lateral area of a cone is 480 pie cm^2.The radius is 40 cm.Find the slant height to the nearest tenth.
12cm
11.5cm
7.7cm
6.7cm

SA = πr^2 + πrl

Question

The lateral area of a cone is 480 pie cm^2.The radius is 40 cm.Find the slant height to the nearest tenth. 
12cm 
11.5cm 
7.7cm
 6.7cm

SA = πr^2 + πrl

anonymous · Answer

SA= 3.14*40^2 + 3.14*40*480
1602.1 +125.6 = 1727.7

doesn't match any of the choices

anonymous · Answer

I got 12.

anonymous · Answer

The reason why it doesn't match up is since you have the formula of the normal surface area. πr² is the base, and lateral area does NOT include the base. Get rid of that and then solve for L.
40πl = 480, but still this doesn't work.
since l ≈ 3.81

anonymous · Answer

LA = pi(r)l

anonymous · Answer

so 480 =rl, or 480 = 40l. Then divide 480/40 so that l = 12