A bag contains 105 red and blue marbles. The ratio of red to blue marbles is 2:5. How many red marbles are in the bag?

30 red marbles

Step-by-step explanation:

If the ratio is 2 red marbles for every 5 blue marbles then you would add them together to find out how many marbles are in one group.

2+5=7

There are 7 marbles in each group.

Now we have to find out how many total groups there are by dividing the total amount of marbles by the amount in each group.

105÷7=15

There are 15 groups of 7 marbles.

Looking back at the ratio, we know that the 15 groups each have 2 red marbles and 5 blue marbles. So if there is 2 red marbles 15 times (2 marbles in 15 groups) we would multiply.

2×15=30

There are 30 red marbles.

I hope that makes sense.

30 people weigh 160 pounds or more