I have 28 marbles in all. Red,Blue, Green. 8 of them are blue. I have 3 times as many red marbles than green marbles. How many are red ?

if 8 marbles are blue then

28 - 8 = 20 are green and red marbles

then if we let x = the number of green marbles,
then the number of red marbles is 3 times the number of green marbles, or 3*x,, and their total sum must be 20:
x + 3*x = 20
combining similar terms,
4x = 20

now solve for x. then get the number of red marbles by multiplying it by 3.

i know that you add frist

To find out how many red marbles there are, let's break down the information given in the question.

We know that you have a total of 28 marbles. Let's assign variables to represent the number of blue, green, and red marbles.

Let B represent the number of blue marbles.
Let G represent the number of green marbles.
Let R represent the number of red marbles.

Now, according to the question, we know that there are 8 blue marbles, so we can write the equation B = 8.

We also know that you have 3 times as many red marbles as green marbles, which can be written as R = 3G.

Finally, we know that the total number of marbles is 28, so we can write the equation B + G + R = 28.

We already have one equation with B = 8, so let's substitute this value into the second equation to eliminate the variable B.

R = 3G (Equation 1)
8 + G + R = 28 (Equation 2)

Substituting B = 8 into Equation 2 gives us:
8 + G + R = 28

Now, substitute the value of R from Equation 1 into Equation 2:
8 + G + 3G = 28

Combine like terms:
8 + 4G = 28

Subtract 8 from both sides:
4G = 20

Divide both sides by 4:
G = 5

Now that we have the value of G (green marbles), we can substitute it back into Equation 1 to find the value of R (red marbles):
R = 3G
R = 3 * 5
R = 15

Hence, there are 15 red marbles.