Since only 1/10 of her income applies to all 5 charities, it would make sense to assume that 1/10 is strictly donated to the charities. Moreover, because we assume that, we must then divide 1/10 by 5, so that way we can get the amount that is donated to each charity. So you should get, 1/50 is equally donated to each charity out of the 1/10 of her income that is donated. Hopefully this helps.
