+1348 In a bag with $20$ marbles, five of them are blue. How many blue marbles must be added to the bag so that the probability of selecting a blue marble at random is $\frac{5}{8}$?
+129771 Let B be the number of blue matbles that we need to add
So
Total Blue / Total Number of marbles = 5/8
[5 + B ] / [ 20 + B ] = 5/8
5 + B = (5/8) ( 20 + B] nultiply both sides by 8/5
8 + (8/5) B = 20 + B
(8/5)B - B = 20 - 8
(3/5)B = 12
B = 12 * (5/3) = 60 / 3 = 20
We need to add 20 blue marbles
Proof
[5 + 20 ] / [ 20 + 20] = 25 / 40 = 5 / 8
+129771 Let B be the number of blue matbles that we need to add
So
Total Blue / Total Number of marbles = 5/8
[5 + B ] / [ 20 + B ] = 5/8
5 + B = (5/8) ( 20 + B] nultiply both sides by 8/5
8 + (8/5) B = 20 + B
(8/5)B - B = 20 - 8
(3/5)B = 12
B = 12 * (5/3) = 60 / 3 = 20
We need to add 20 blue marbles
Proof
[5 + 20 ] / [ 20 + 20] = 25 / 40 = 5 / 8
