A bag contains blue marbles and red marbles, 42 in total. The number of blue marbles is 3 less than 4 times the number of red marbles. How many blue marbles are there?

The number of blue marbles = 33

Step-by-step explanation:

Let b represent blue marbles and r represent red marbles

there are b + r = 42 marbles in total

The number of number of blue marbles is 3 less than 4 times the number of red marbles

we can express it as b = 4r - 3

Since there are b + r = 42 marbles in total and b = 4r - 3 we can rewrite the equation

b + r = 42

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r + 4r - 3 = 42

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5r - 3 = 42

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5r = 45

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r = 9 The number of red marbles = 9

The number of blue marbles 42 - 9 = 33