Changes

:The [[isotope]] took 20 seconds [[second]]s to half in [[Count Rate|count rate]]::'''Half life''' = 20 [[second]]s.

2. Predict the [[Count Rate|count rate]] at 90 seconds[[second]]s.:Since the '''half life''' is 20 seconds [[second]]s the [[Count Rate|count rate]] 20 seconds [[second]]s earlier can be halved. :At 70 seconds [[second]]s the [[Count Rate|count rate]] was 88Bq. Therefore at 90 seconds [[second]]s the [[Count Rate|count rate]] would be:

3. Predict what the [[Count Rate|count rate]] was 10 seconds [[second]]s before the [[sample]] was first tested.:Since the '''half life''' is 20 seconds [[second]]s the [[Count Rate|count rate]] 20 seconds [[second]]s later can be doubled. :At 10 seconds [[second]]s the [[Count Rate|count rate]] was 707Bq. Therefore at -10 seconds [[second]]s the [[Count Rate|count rate]] would have been:

:The [[isotope]] took 20 seconds [[second]]s to half in [[Count Rate|count rate]]::'''Half life''' = 20 [[secondssecond]]s.

2. Predict the [[Count Rate|count rate]] at 90 seconds[[second]]s.:Since the '''half life''' is 20 seconds [[second]]s the [[Count Rate|count rate]] 20 seconds [[second]]s earlier can be halved. :At 70 seconds [[second]]s the [[Count Rate|count rate]] was 88Bq. Therefore at 90 seconds [[second]]s the [[Count Rate|count rate]] would be:

3. Predict what the [[Count Rate|count rate]] was 10 seconds [[second]]s before the [[sample]] was first tested.:Since the '''half life''' is 20 seconds [[second]]s the [[Count Rate|count rate]] 20 seconds [[second]]s later can be doubled. :At 10 seconds [[second]]s the [[Count Rate|count rate]] was 707Bq. Therefore at -10 seconds [[second]]s the [[Count Rate|count rate]] would have been: