Display Case

In a display case with 21 ribbons , one -third are blue and two-thirds are pink. To obtain a display case in w

In a display case with 21 ribbons , one -third are blue and two-thirds are pink. To obtain a display case in which one quarter are blue, how many pink should be added ?

Okay, there are currently (2/3)21 = 14 pink.
And if 1/4 are to be blue, then (3/4) need to be pink.
So, letting x be number of pink to be added, then
(14+x)/(21+x) = 3/4.
Or, cross multiplying, 56+4x=63+3x, or
x=7.
So, 7 pinks should be added.

Plano display case.wmv