math,(fraction)
posted by Da S on .
Mr Lim put some red pens and blue pens into a box.The ratio of the number of red pens to the number of blue pens was 3:4.
He added 20 red pens into the box and the ratio became 2:1.
a. were there more red pens or blue pens in the box at the end?
b. how many red pens were there in the end?
c. how many blue pens were there?

well, since the ratio r:b = 2:1 I'd say there were more r's...
(r+20)/b = 2/1
r/b = 3/4
so, b = 4/3 r
(r+20)/(4/3 r) = 2
r+20 = 8/3 r
5/3 r = 20
r = 12
so, there were 32 reds at the end
there were 4/3*12 = 16 blue pens. Note that 16 = 32/2 as well. 
I don't know my mom