Aballoon filled with helium gas has an average density of

Average density is defined by following formula

here in order to find out the average density of helium we can fill a balloon of helium gas and then we can find it's volume and its mass.

The ratio of mass and volume of that balloon will help us to find the average density of helium

So by the above experiment the average density of helium is approx 0.179 kg/m^3.

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form

no. bullets are macro objects. wave nature is for light waves, extremely tiny particles. if a light particle was the size of your finger, the bullet would be the size of the universe. so basically, that huge difference in size makes the wave nature of matter insignificant.