Math
posted by peter .
to identical jars are filled with equal amount of marbles. the marbles are coloured red or white. the ratio of red to white marblesis 7:1 in jar 1 and 9:1 in jar 2. if there are 90 white marbles altogether, determine the number of red marbles in jar 2.

R1/W1 = 7
R2/W2 = 9
W1 + W2 = 90
R1 + W1 = R2 + W2
Four equations in four unknowns.
Change the last equation by substitution to get rid of R1 and R2.
7W1 + W1= 9W2 + W2
8W1  10 W2 = 0
10W1 + 10W2 = 900
18 W1 = 900
W1 = 50
R1 = 350
W2 = 40
R2 = 360
There are 360 red marbles in jar 2