PC disks

Peter has 45 disks in three colors. One-fifth of the disks are blue; red is twice more than white. How many blue, red, and white disks are there?

Correct answer:

b =  12
c =  24
m =  9

Step-by-step explanation:


m+c+b=45
m=45/5
c = 2b

m+c+b=45
m=45/5
c = 2·b

b+c+m = 45
5m = 45
2b-c = 0

Pivot: Row 1 ↔ Row 3
2b-c = 0
5m = 45
b+c+m = 45

Row 3 - 1/2 · Row 1 → Row 3
2b-c = 0
5m = 45
1.5c+m = 45

Pivot: Row 2 ↔ Row 3
2b-c = 0
1.5c+m = 45
5m = 45


m = 45/5 = 9
c = 45-m/1.5 = 45-9/1.5 = 24
b = 0+c/2 = 0+24/2 = 12

b = 12
c = 24
m = 9

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