Acertain element has a half life of 4.5 billion years. a. you find a rock containing a mixture of the element and lead. you determine that 60% of the original element remains; the other 40% decayed into lead. how old is the rock? b. analysis of another rock shows that it contains 5% of its original element; the other 95% decayed into lead. how old is the rock?

Step-by-step explanation:

8.5 billion years old is answer

step-by-step explanation:

their are no angles. sorry cant .

percentage - 25%

probability - 0.25

we know,

total amount of students in class = 20

total boys = 10

total girls = 10

no of girls who wear glasses = 10/2 = 5

probability of choosing a girl with glasses is =

number of girls wearing glasses/total number of students in the class = 5/20

thus, percentage of selecting a girl wearing glasses will be

= 5/20 × 100

= 5 × 5

25%

therefore,

probability will be 0.25

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