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## Homework Statement

A sample of sodium pertechnetate injection was found to have an activity of 51439 counts per minute (cpm). The sample was measured again exactly after 8 hours and found to have an activity of 20476 cpm. Calculate the half life of sodium pertechnatate.

## Homework Equations

A = A0 e^-lamdat

ln A = in A0 - lamdat

half life = ln2/lamda

## The Attempt at a Solution

ln 20476 = ln 51439 -lamda * 8

9.927008748 = 10.84815192 - lamda * 8

0.9150875487/8 = -lamda

lamda = 0.1143859436

half life = 6.06 hours

Is this correct? I think I did the algebra a bit wrong but the answer of 6 hours sounds about right... can anyone help please...thanks.