Easy quant question; Can somebody explain?

[Jamesdc]

A local bank reports that 80% of its customers maintain a checking account, 50% have a savings account, and 40% have both. If a customer is chosen at random, what is the probability the customer has only one account, either a checking account or a savings account?

 

[dinesh.sundrani]

Think Venn Diagram for this..
80 customers are having Checking Account
50 customers are having Saving Account
40 are having both
therefore,
Customers only having Checking Account are = 80 - 40 = 40
Customers only having Saving Account are = 50 - 40 = 10
Total customers have just one account (be it Saving or Checking, we don’t care) = 40 + 10 = 50
So out of total 100 customers, 50 are having just 1 account. Hence probablilty should be 50/100 = 0.5
- Dinesh S

 

[florinpop]

dinesh is right or you can think of it like this
40% have both that means that 60% have one or none
1-80%=20% percentage of ones that dont have savings
1-50%=50% percentge that don’t have checking
0.2*0.5=10% percentage that have either
60%-10%=50% percentage that have at least one acc

 

[Jamesdc]

Thanks Dinesh