What is the units digit of 1!+3!+5!+7!+9!+11!?

Just add up the first two and the rest of them end in zeros:

1! + 3! =1 + 6 =7 - the units digit.

See, since 5! ends in a zero, all the factorials after that end in a zero! Test it out, yourself. Therefore, 1! ends in 1, and 3! ends in 6. Thus, 1+6+0+0+0+0=7.