Step-by-step explanation:
I don't know what the 3rd fruit is. let's call it an apple.
so,
1 apple + 3 cherries = 3 bananas
1 apple = 3 bananas - 3 cherries
1 banana + 2 cherries = 1 apple = 3 bananas - 3 cherries
5 cherries = 2 bananas
1 apple + 1 banana = (1 banana + 2 cherries) + 1 banana =
= 2 bananas + 2 cherries =
= 5 cherries + 2 cherries =
= 7 cherries
the numbers did not help, as they were wrong.
e.g. if you assume the apple = 5, a cherry = 1 and a banana = 2, you would get 8 = 6 on the first scale.
if you change the apple to a 3, that would make the first scale true (6 = 6), but the second scale wrong (4 = 3).
funny enough, the other answer got 7 nevertheless (but the wrong way - actually 2 mistakes balanced each other out).
it is 7 cherries, though !
the actual numbers would be e.g.
a cherry = 1
then
1 banana = 5/2 = 2.5
1 apple = 3×5/2 - 3 = 15/2 - 6/2 = 9/2 = 4.5
to get whole numbers, we could multiply all by 2 :
cherry = 2
banana = 5
apple = 9
and then the first balance :
9 + 3×2 = 3×5
9 + 6 = 15
15 = 15 correct
the second balance
5 + 2×2 = 9
9 = 9 correct.
