My last question of the night..please help

The intensity I of light bulb varies inversely as the square of the distance d from the light bulb. Suppose I is 250 w/m^2 when the distance is 5 m. How much farther would it be to a point where the intensity is 40 w/m^2?

Question

My last question of the night..please help

The intensity I of light bulb varies inversely as the square of the distance d from the light bulb.  Suppose I is 250 w/m^2 when the distance is 5 m.  How much farther would it be to a point where the intensity is 40 w/m^2?

anonymous · Answer

250 : 5
1: 1250
x : 40
x = 31.25m

anonymous · Answer

I1= 250 
I 2 = 40 

D1= 5M
D2=?
$$I1\div I2$$=$$D2 ^{2} \div D1^{2}$$
$$250 \div 40 =D2^{2}\div25$$
$$D2 =12.5 M$$