Assalaamu alaykum wa rahmatullaahi wa barakaatuhu, Shaykh. Is the reward of every good deed multiplied by ten times when a person does that good deed in the state of fasting? May Allaah reward you, Shaykh.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

All acts of obedience, if one does them for the sake of Allah, their reward will be multiplied ten times, and they may be multiplied until seven hundred times regardless of whether the doer is fasting or not fasting.

The ahaadeeth are general in regard to the multiplication of rewards.

Abu Hurayrah, may Allah be pleased with him, narrated that the Prophet said, "Allah says, 'If My slave intends to do a bad deed, then (O Angels) do not write it down unless he does it; if he does it, then write it as it is (i.e. as one bad deed), but if he refrains from doing it for My sake, then write it as a good deed (in his account). (On the other hand) if he intends to do a good deed but does not do it, then write it as one good deed (in his account); and if he does do it, then write it for him (in his account) as ten good deeds up to seven-hundred times." [Al-Bukhaari and Muslim]

As for fasting itself, then it is only Allah Who knows its reward and how many times it is multiplied.

Abu Hurayrah, may Allah be pleased with him, narrated that the Prophet said, "Every (good) deed of the son of Adam will be multiplied ten times to seven hundred times in reward. Allah, the Exalted, has said: 'With the exception of fasting, for it is done for Me (My sake) and I will reward it…" [Al-Bukhaari and Muslim]

Allah knows best.