Decaffeinated coffee = 1/3
Regular coffee = 2/3
"Of those who do not drink decaf, 2/5 add cream to their coffee."
means 'of the regular drinkers, i.e. of the 2/3, 2/5 add cream' that means 3/5 0f 2/3 don't add cream.
And the answer becomes = 3/5(2/3)= 2/5n
wats wrong with this approach?
Your approach is correct for one part of the answer.
Of the regular coffee drinkers, 3/5 do not add cream so we get that (2/5)n drink regular coffee without cream. But is this the fraction they are looking for?
They are looking for 'the number of employees who do not drink 'regular coffee with cream.'
i.e. the number of employee who drink either 'decaf' or 'regular coffee without cream' or 'some other non-regular coffee' or 'no coffee'.
We are looking for people who do not drink 'regular coffee with cream'.
The question tells us that there are no people who drink 'some other non-regular coffee' or 'no coffee'.
You calculated that no. of people who drink 'regular coffee without cream' = (2/5)n
No of people who drink decaf = (1/3)n
No of people who do not drink 'regular coffee with cream' = (1/3)n + (2/5)n = (11/15)n
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