A bag contains 120 marbles. Some are red and the rest are black. There are 19 red marbles for every black marble. How many red marbles are in the bag?

114 red marbles

Step-by-step explanation:

red: black: total

19      1        19+1 = 20

We have 120 marbles

120/20 = 6

Multiply each  by 6

red: black: total

19 *6   1*6  20*6

114         6       120

There are 114 red marbles.

Step-by-step explanation:

We can make a smaller sample of the problem to help evaluate the big one. For every 19 red, there is 1 black. That means the sample size is 20 in total since 19+1 is 20. In other words, for every 20 marbles, 19 of them are red.

Now we can look at the size of 120. 20 goes into 120 6 times. That means there are 6 times as many red marbles. 19x6=114.

There are 114 red marbles.

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