There are 61 blue marbles
Solution:
Let "b" be the number of blue marbles
Let "r" be the number of red marbles
Given that bag contains blue marbles and red marbles, 75 in total
number of blue marbles + number of red marbles = 75
b + r = 75 -------- eqn 1
The number of blue marbles is 5 more than 4 times the number of red marbles
number of blue marbles = 5 + 4(number of red marbles)
b = 5 + 4r ------- eqn 2
Let us solve eqn 1 and eqn 2
Substitute eqn 2 in eqn 1
5 + 4r + r = 75
5 + 5r = 75
5r = 75 - 5
5r = 70
r = 14
From eqn 2,
b = 5 + 4(14) = 5 + 56 = 61
b = 61
Thus there are 61 blue marbles