Question

the ratio of red marbles to blue marbles in a bag is 4:7. There are 16 red marbles.How many blue marbles are there? solve for indicated variable.

Answer 1

red marbles : blue marbles = 4:7

16 - red marbles
x - blue marbles

$\frac{16}{x}=\frac{4}{7} \\ 16 \times 7 = 4x \\ 4 \times 7 = x \\ x=28$

There are 28 blue marbles.

Answer 2

4x - number of red marbles
7x - number of blue marbles

$4x=16\\ x=4\\\\ 7x=7\cdot4=\boxed{28} \leftarrow \hbox{number of blue marbles}$