Answer:
40/9
Step-by-step explanation:
Use the work formula,
+
=
, where A is the amount of time it takes one person, B is the amount of time it takes another person, and T is the time it takes for them to work together.
Plug in the times for David and Alex alone:
+
= 
Find the least common denominator, which is 40.
+
= 
= 
Cross multiply and solve for T:
9T = 40
T = 40/9
So, if they worked together, it would take them 40/9 hours
Answer:
1150%
Step-by-step explanation:
The percentage change is ...
percentage change = (amount of change)/(original amount) × 100%
= ((new amount) - (original amount))/(original amount) × 100%
= ($1250 -$100)/$100 × 100%
= 1150/100 × 100%
= 1150%
I want to say the third option but dont trust my opinion
Note that there's a strict order here -> 2 close friends, then 1 non-close friend.
So, picking in order:
probability of picking the first close friend: 4/10
probability of picking the second close friend: 3/9
probability of picking the first non-close friend: 6/8
So, we get 4/10 * 3/9 * 6/8 = 1/10.