In a bag containing only blue, red and green marbles, all but 15 are blue, all but13 are red and all but 12 are green. How many are red?1. 132. 73. 254. 20

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted on

Lets say we have ;

X red balls

Y green balls

Z blue balls


All but blue means the number of balls except blue balls.Others are also same as this.


all but 15 are blue

So we can w write  X+Y = 15-----(1)


all but 13 are red

So we can w write  Z+Y = 13-----(2)


all but 12 are green

So we can w write  X+Z = 12-----(3)


By solving (1),(2) and (3) we will have;

X = 7

Y = 8

Z = 5


So number of red balls is 7.

Answer is (2)



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