Significant. Depending on part of your cycle you have sex.
High. Very unreliable method of birth control - also increases your chance of sexually transmitted diseases.
What are chances of getting pregnant using pullout method right before ovulation. And sex with another guy during ovulation with ejaculation.?
High. Any unprotected sex during ovulation is a set up for pregnancy, pure and simple. It doesn't matter which guy it is with. Sperm is sperm.