Question

A wall is made of both red and yellow bricks. The ratio of red bricks to yellow bricks 5:2.
If there are 210 more red brick then yellow, how many bricks are in the wall?

Answer 1

For every 5 red bricks there are 2 yellow bricks.

Yellow = X
Red = X + 210

Since the red:yellow ratio doesn't change, (5/2) = (210+X)/X

Cross multiplying gets you 5X = 2(210+X). Solve for X. Once you know how many yellow and red bricks there are, add them up and you have the total.

Answer 2

why did you put the red bricks/yellow bricks?

Answer 3

It could be the other way around, it's just a ratio.

You could also say instead of a 5:2 ratio it's 2.5:1 ratio. Then for X yellow bricks you have 2.5X red bricks.

2.5X = 210 + X.

If you solve for the original equation:
5X = 420 + 2X
2(2.5X) = 2(210 + X)

Same equation.