This is a good example of what you believe you read verses what you actually read.

 

This appears to say 7 pairs of each clean animals and two pairs of all unclean animals, it also appears that it says seven pairs of every kind of bird.  They came onboard the Ark two by two which could explain why most believe there were two of each animal and bird.

 

Genesis 7
1.The LORD then said to Noah, "Go into the ark, you and your whole family, because I have found you righteous in this generation.
2.Take with you seven of every kind of clean animal, a male and its mate, and two of every kind of unclean animal, a male and its mate,
3.and also seven of every kind of bird, male and female, to keep their various kinds alive throughout the earth.

8.Pairs of clean and unclean animals, of birds and of all creatures that move along the ground,
9.male and female, came to Noah and entered the ark, as God had commanded Noah.

Sources of information: Holy Bible.