A box contains 60 identical marbles where x of them are red while the rest are yellow. If a marble is drawn and the probability that it is white is 1/12, find the value of x. b: How many white marbles must be added to the box so that the probability of choosing a white marble is 5/16?
Please answer I will make brianliest!!

a. x is 55

b. 20 white marbles

Step-by-step explanation:

Question: A box contains 60 identical marbles where 'x' of them are red while the rest are white; (given that in the original question, the box only contains red and yellow marbles, the yellow can be replaced by white to explain the question idea)

a. The number of identical marbles in the box, n = 60

The number of red marbles = x

The number of white marbles = The rest of the marbles which are not red

The probability that a marble drawn is white, P(y) = 1/12

Let 'y' represent the number of white marbles

From probability theory, we have;

The number of white marbles, y = n × P(y) = 60 × 1/12 = 5

The number of red marbles, x = n - y = 60 - 5 = 55

x = 55

b. The number of white marbles that must be added to make the probability of choosing a white marble = 5/16 is given as follows;

Let Δy represent the number of white marbles added, therefore;

P(y) = (y + Δy)/(y + Δy + x)

∴ P(y) = (5 + Δy)/(5 + Δy + 55) = 5/16

5 × (60 + Δy) = 16 × (5 + Δy)

300 + 5·Δy = 80 + 16·Δy

16·Δy - 5·Δy = 300 - 80

11·Δy = 220

Δy = 220/11 = 20

The number of white marbles that must be added, Δy = 20 white marbles

hello,

b) 62.47% of the students are between 14 and 18 years old.

step-by-step explanation:

mean = 15 and standard deviation = 2

student between 14 to 18

formula used z-score

for age 14 , z score

using z-table , p(z> -0.5)=0.3085

for age 18 , z score

using z-table , p(z< 1.5)=0.9332

p(-0.5< z< 1.5)=0.9332-0.3085 = 0.6247

thus, 62.47% of the students are between 14 and 18 years old.

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