Ms. Watson's age is 5 years more than 2 1/2 times her son's age. She is 55 years old. How old is her son, in years?
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Given:
Total number of calculators in a box = 10
Defective calculators in the box = 1
To find:
The number of ways in which four calculators be selected and one of the four calculator is defective.
Solution:
We have,
Total calculators = 10
Defective calculators = 1
Then, Non-defective calculator = 10-1 = 9
Out of 4 selected calculators 1 should be defective. So, 3 calculators are selected from 9 non-defective calculators and 1 is selected from the defective calculator.
Therefore, the four calculators can be selected in 84 ways.