[blueunicorn6]

How many Japanese troops were used to defeat that Allied force of 151,000 Soldiers? Most military theory says the attackers need to be three times larger than the defenders. We were defending. Did the Japanese attack with 500,000 troops?

[buwaya]

No.
The Japanese attacked Luzon with two divisions, an independent brigade, and two tank regiments, plus various supporting artillery, etc.
Luzon was defended by @ 90,000 Filipino and US troops in, nominally, one US division (understrength, 2/3 Philippine scouts), 9 Philippine Army divisions (all about regiment-sized, effectively), one battalion sized Scout cavalry regiment and one battalion sized Marine regiment, and two tank groups.
There were also a very large number of support, fortress, Navy and USAAF personnel, but these were not combat troops.
The big difference is that the Philippine troops could not be expected to hold anywhere by themselves unless concentrated in overwhelming numbers, and that because the Japanese could land anywhere, there were no positions they could be expected to hold, unless it was the short Bataan front. There were only the equivalent of 10 US/Scout infantry battalions that were combat effective in Dec 1941. That’s why Philippine defense reverted to War Plan Orange-3.

[fso301]

How many Japanese troops were used to defeat that Allied force of 151,000 Soldiers?

USAFFE didn't have that many men.

[5th MEB]

Please do not forget; defenders also need adequate supply and logistic lines in order to be successful against a numerically superior attacking force, that can be reinforced and resupplied at any time.
Supplies were not adequate at Corrigador at the time of the attack, and the logistic support line simply did not exist.
Can't think of a better prescription for disaster for a defending force right off the top of my head.