Therefore, it is only necessary to calculate the sum of the probabilities of twice drawing weighted coins and twice drawing heads.

1. even selected.

The probability is

( 1/2)

When the probability of two heads (1/2) 2

So the probability that even numbers are taken out twice is (1/2) 3 = 1/8.

2.

I chose weighting.

The probability is

( 1/2)

Probability of being caught for the first two times (0.2) 2

So the probability that even numbers are taken out twice as heads is (1/2) * 0.2 2 = 0.02.

Therefore, considering that both coin flips are heads up, it is possible to choose a coin with weight.

Is 0.02/(1/8+0.02) = 0.1379.