# Thread: Math Test Question

1. ## Math Test Question

A Lab has a 500g sample of nitrogen. The substance has a half life of about 10 minutes.

Write a formula to express this.... I think I got this answer

V=500(250)^10

How much nitrogen is left after 30 min?

How much is left after an hour?

2. Originally Posted by Cdawson

V=500(250)^10
Where did the 250 come from?

3. 250^10 = 953,674,316,406,250,000,000,000

4. Originally Posted by Cdawson
A Lab has a 500g sample of nitrogen. The substance has a half life of about 10 minutes.

Write a formula to express this.... I think I got this answer

V=500(250)^10

How much nitrogen is left after 30 min?

How much is left after an hour?
the general equation for decay problem:
V=A(r)^n
A= sample start
r = rate of decay
n = period

in this case,
V=A(r)^n
A= 500
r = 0.5
n = 1 (1 = 10 minute)
$V=500 (0.5)^1$

how many after 30 minutes??
V=A(r)^n
A= 500
r = 0.5
n = 3 (1 = 10 minute)
$V=500 (0.5)^3$

how many after 1 hour???
(hint: you just convert hour to minute it would be the n)

....hope it help....