The Two Trees

Probability Level 1

There are 2 trees in a garden (tree A and B ) and on the both trees are some birds.

The birds of tree A say to the birds of tree B that if one of you comes to our tree, then our population will be the double of yours.

Then the birds of tree B tell to the birds of tree A that if one of you comes here, then our population will be equal to that of yours.

Now answer: How many birds on each tree ?

This problem is a part of the set brain games

7 on A , 5 on B 5 on A , 5 on B 7 on A , 7 on B 5 on A , 7 on B

2 solutions

Arpan Sarangi
Jul 16, 2015

An easy question made more easy with options!!

Raam Songara
Feb 20, 2015

Tree A = a

Tree B = b

So a + 1 = 2(b - 1) (1)

and a - 1 = b + 1 (2)

so a = b + 2 (3 by re-arranging 2)

Therefore b + 2 + 1 = 2b - 2 ( Sub 3 into 1)

and 2b - b = 2 + 2 + 1

so b = 5

(sub 'b' into 3)

a = 5 + 2 = 7

Therefore Tree A has 7 birds and Tree B has 5 sorry for long-winded answer