Probability
posted by Amponsah .
A bag contains some balls of which 1/4 are red. Forty more balls of which 5 are red are added. If 1/5 of all the balls are red, how many balls was there originary?

Probability 
Reiny
original number of balls  x
original number of red balls = x/4
number of red balls added = 5
total balls added = 45
new total = x+45
new red ball total = (x/4 + 5)
(1/5)(x + 45) = x/4 + 5
x/5 + 9 = x/4 + 5
times 20
4x + 180 = 5x + 100
x = 80
you had 80 balls
check:
you had 80 of which 20 were red
you added 45 of which 5 were red
new total 125
new number of red = 25
is 25 equal to 1/5 of 125 ? YES!!
Respond to this Question
Similar Questions

Finite Math
An urn contains sixteen red balls and seventeen white balls. A sample of three balls is selected at random and the number of red balls observed. Determine the probability distribution for this experiment: Number of Red Balls/Probability … 
Finite MathProbability
Suppose we have an urn with 10 white balls and 6 red balls, and we create an experiment by randomly selecting 6 balls from the urn. a) What is the probability that the sample has the same number of white balls as red balls? 
Basic Mathematics
A bag contains 2 red balls, 3 blue balls and 5 green balls. 3 balls are drawn at random. Find the probability that a) the 3 balls are of different colours b) 2 balls are of the same colour c) all the 3 are of the same colour. 
Math
A bag contains three black balls, four white balls and five red balls. Three balls are removed without replacement. What is the probability of obtaining a one of each colour b at least two red balls ? 
Statistics HELP
There are two bags each containing red balls and yellow balls. Bag A contains 1 red and 4 yellow balls. Bag B contains 3 red and 13 yellow balls. Alva says that if we choose one bag and draw one ball from that bag you should always … 
Pre Algebra Probability
Each of two urns contains green balls and red balls. urn 1 contains 10 green balls and 14 red balls. urn 2 contains 4 green balls and 11 red balls. if a ball is drawn from each urn what is p(red and red)? 
Math help?
I am kind of stuck on this one Each of two urns contains green balls and red balls. Urn I contains 10 green balls and 8 red balls. Urn II contains 3 green balls and 10 red balls. If a ball is drawn from each urn, what is P(red and … 
Another math related question
Two urns both contain green balls and red balls. Urn 1 contains 6 green balls and 4 red balls and urn 2 contains 8 green balls and 7 red balls. A ball is drawn from each urn.What is the probability that both balls are red 
GEOMETRY
from a bag containing 6 white balls, 3 black balls and 13 red balls, two balls are drawn at random. what is the probability that they are both red? 
Maths
A bag contains 18 balls out of which x balls are red balls will be 9/8 times the probability of not drawing red balls. Find value of x .