So in this problem we need to do some addition.
take the starting balance (-200) and add it to the amount you paid back (30)
-200 + 30 = -170
305 plus 90= 395. Found by doing 395-90
A suitable statistics calculator gives the probability that 6 or more show up as being about ...
0.2539
You would use cross multiplication:
X/2,000 = 3/5
Multiply: 2,000*3= 6,000
Divide: 6,000/5
Answer: 1,200 doctors use brand x
The correct answer is 10/15, simplified to 2/3.