Core 4 Integration help please?

Question

The mass, m g, of a radioactive substance at time t seconds, is such that dm/dt = -m  When t= 0, m = 4

a) Find the mass when t = 0.5

Thanks for any help, I'm just lost again!

Answer 1

Step 1 :

The equation is and when .

Rewrite the above equation :

Apply integration on each side.

When .

Substitute in equation (1).

Substitute in above equation.

when

Solution :

when