## mariadelia27 2 years ago A 10 gram sample of a substance that's used to detect explosives has a k-value of 0.1353. Find the subtance's half-life, in days.round to the nearest hundreds

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1. RaphaelFilgueiras

you shoud try to ask it in chemistry section

ok thanks it scause i really need this answer

3. RaphaelFilgueiras

do you have the formula?

n=Noe^kt

5. RaphaelFilgueiras

n is moles?

i need to round to the nearest hundreds too

7. RaphaelFilgueiras

what is the unity of k?

8. swissgirl

What does k represent?

a positive constant that depends on the substance itself and on the units used to measure time

10. RaphaelFilgueiras

5=10*e^(Kt), but what unity of time? seconds^-1?

11. swissgirl

Its in days

there a picture of the question

13. RaphaelFilgueiras

and probally the formula is e^(-kt)

did you see the picture

15. swissgirl

ya its a diff question :)

my bad ill got teh wrong one

17. RaphaelFilgueiras

if k is in days^-1 just solve 5=10*e^(-kt), and you will find t

but i dont know how to solve it either -.-

can you help me please i really need it

20. RaphaelFilgueiras

ok

21. RaphaelFilgueiras

|dw:1372309018511:dw|

its exponoential decay thats the section were doing

24. RaphaelFilgueiras

5.12303

25. RaphaelFilgueiras

k=0.1353

26. RaphaelFilgueiras

i use that k

yeah k is that

0.1353

it said its wrong -.-

30. RaphaelFilgueiras

we have to know thr unity of k

31. swissgirl

What did you put the answer as?

32. swissgirl

sorry I am not making sense. What did you enter as your answer?

5.12303

34. swissgirl

Its to the hundredths place so it should be 5.12

35. RaphaelFilgueiras

try 1871.15 days

36. RaphaelFilgueiras

im supposing k is in years

37. swissgirl

Ohhhh yaaaaa that makes more sense actually

just that its 53% not 51 %

this is another question can you guys help with this one

you guys help me i really did to passs this class tomorrow is my last day

are you guys there ?

heeelp anyone

45. RaphaelFilgueiras

6733.44 years