Answer: 11


Using a table
2 children together eat the same as Ma Bean

Ma Bean	2		6	8
Ma + 2 children	4	8	12	16	20
Pa Bean	19	15	11	7	3
Comment	Pa eats more than half		Good	Ma eats more than Pa

Using reasoning
Pa Bean does not eat more than half the beans, so he eats at most 11 beans. Ma Bean eats the same number of beans as both children together, so she eats an even number of beans that is at least one quarter of the total number of beans eaten. Therefore she eats at least 6 beans. If she does eat 6 beans, then Pa Bean eats 11 beans, which is consistent with the information given. However, if Ma Bean eats 8 or more beans, then Pa Bean eats at most 7 beans and this is impossible as we are told that Pa Bean eats more beans than Ma Bean. So Pa Bean eats 11 beans.