Rom 5:12 Wherefore, as by one man sin entered into the world, and death by sin...How is it that Adam's sin passed to Eve when it appears that Eve ate the fruit first?
Genesis 3:6 "When the woman saw that the fruit of the tree was good for food and pleasing to the eye, and also desirable for gaining wisdom, she took some and ate it. She also gave some to her husband, who was with her, and he ate it."
Adam was right there listening to the serpent, knowing that what the serpent said was a lie and he made no attempt to challenge it.
Maybe he was just waiting for an opportunity like this to present itself.
He was very quick to put the blame on Eve and on God.
"The woman - That YOU gave me, SHE gave me the fruit and I ate it."
And of course there is the question of what they were doing at the tree in the first place.
I have always found it interesting that Eve got a curse and a blessing and all Adam got was a curse.