A bag contains white marbles and red marbles, 31 in total. The number of white marbles is 9 less than 4 times the number of red marbles. How many white marbles are there?

There are 23 white marbles.

Step-by-step explanation:

To find the number of white marbles that are there in the bag, we will first write represent the question in a mathematical format, then solve

Let w represent the number of white marbles    and  let r represent the number of red marbles

From the question given;

"A bag contains white marbles and red marbles"   can be represented mathematically as

w + r = 31 (1)

" The number of white marbles is 9 less than 4 times the number of red marbles"      can be represented mathematically as

w = 4r - 9  (2)

We can now solve equation (1)  and equation (2) using substitution method

substitute equation (2) in equation (1)

4r - 9 + r =31

5r - 9 = 31

add 9 to both-side of the equation

5r - 9 + 9 = 31 + 9

5r =40

Divide both-side of the equation by 5

5r/5 = 40/5

r = 8

substitute r=8 in equation (1)

w + r = 31

w + 8 = 31

subtract 8 from both-side of the equation

w + 8 - 8 = 31 - 8

w =23

There are 23 white marbles.