Strontium-90 has a half-life of about 29 years. After 65 years, about how many grams of a 25-gram sample will remain?
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Answer:
There must be 35 red marbles.
Step-by-step explanation:
This question can be solved using a rule of three.
A probability is the number of desired outcomes divided by the number of total outcomes.
The probability of randomly choosing a red marble is 7/9.
This means that for each set of 9 marbles, 7 must be red.
There are 45 marbles in total in the bag and each is equally likely to be chosen. Work out how many red marbles there must be.
How many red marbles out of 45?
7 red - 9 marbles
x red - 45 marbles
Simplifying by 9
There must be 35 red marbles.