Can u solve this Math question?

"A" speaks truth in 75% cases n "B" in 80% cases.In what % of cases are they likely to contradict each other,narrating the same incident? a)5% b)15% c)35% d)45% The ans is 35% can anyone explain how n why??

Relevance
• Anonymous
9 years ago

The way I read it, you want the probability of them contradicting each other. This can occurs in two ways, either

A.)Person A tells the truth (75% chance) and B lies (20% chance)

OR

B.)Person A lies (25% chance) and person B tells the truth (80% chance)

To find the total chance, you find the chance of either of those events occurring then add them together. So,

Chance of event A occurring=.75*.20=.15

Chance of event B occurring=.25*.8=.2

So added together, Chance A+Chance B=.35 or 35%. Does that make sense?

• 9 years ago

If A speaks the truth, there is a 15% chance B will be contradicting because 3/4 * 1/5 = 3/20 = 15%

If B speaks the truth, there is a 20% chance A will be contradicting because 4/5 * 1/4 = 4/20 = 20%

15 + 20 = 35%

• 9 years ago

Here is what i think:

for them to contradict each other either A says a truth and B lies or A lies and B says a truth.

For the first case (A truth, B lie) , the probability is:

.75*(1-.8)=.75*.2=.15

For the second case (A lie, B truth):

(1-.75)*.8=.25*.8=.2

So there is a 15% chance of case 1 and a 20% chance of case 2. But you want to know the total:

15%+20%=35%

This is what I would think just using logic.