Answer:
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.