Question

How Many Oranges?
All oranges have equal weight. The two papayas have the same weight. The weights in the first and second balances are equal.
How many oranges balance the weight in the third?

Answer 1

In the first balance, we see that the total of weight of 3 oranges is equal to the combined weights of an orange and a mango. As all the oranges are of the same weight, we can say that the weight of a mango is equal to the weight of 2 oranges.
In the second balance, we see that the total weight of 2 papayas is equal to the combined weights of 2 oranges and a mango. But as two oranges and a mango weigh the same, we can say that the weight of 2 papayas is equal to the weight of 2 mangoes. Thus, the weight of each papaya is equal to the weight of each mango and the weight of a mango is equal to the weight of 2 oranges. Therefore in the third balance, we need 4 oranges on the right pan of the balance in order to have equal weights on both the sides.