#### xMaFF

##### Member

- Joined
- Jun 8, 2009

- Messages
- 173

- Gender
- Male

- HSC
- 2011

Just need help with solving 'half-life' questions for growth and decay.

There are 3 questions, ranking from 1-3 of importance that I would like to receive assistance with.

Any help is very much appreciated!

*(Question 1):*

A radioactive material is decaying exponentially. The rate of change in the mass of the radioactive material is proportional to the mass. If in 3 years a mass of 60g reduces to 40g, FIND ITS HALF-LIFE.

*(Question 2):*

The decay of radium is proportional to its mass. If 100kg of radium takes 5 years to decay to 95kg, FIND ITS HALF-LIFE.

And finally,

*(Question 3):*

If N=400e^(-0.4t), find t when N is HALF its initial value.

Thank you in advance to those who contribute!