There are total of 63 bikes in a store. if the ratio of blue bikes to red bikes is 4 to 5, how many of the bikes are blue?

4x- blue
5x- black.
4x + 5x = 63
9x = 63
X = 7
Bikes that are blue - (4x) -> 4(7) = 28
Bikes that are black - (5x) -> 5(7)= 35
Answer- 28 blue bikes.
Hope this helps.

Let B be the blue bikes and R the red bikes

B/R = 4/5 (given)   and B+R = 63 (given). To find the # of blue bikes.

Remember that : a/b = c/d could also be written in keeping the equality as:

(a+b)/b = (c+ d)/d

B/R = 4/5
(B+R)/R = (4+5)/5
but B+R = 63
63/R = 9/5 (cross multiplication:

9R = 5 x 63 → 5R = 315    and R =  35 Red bikes
Blue bikes = 63 - 35 →Blue Bikes = 28