Perfect use for condoms has a 2% failure rate. Perfect use means the user did nothing wrong, not that the condom was perfect.
0.98 ^ 35 = 0.49, i.e. 51% chance of failure.
Failure here means child conceived. And keep in mind that there is only approximately a 2% chance of having a child from each encounter, so condoms fail a LOT. (20% chance of a child if done at the right time divided by 3 days out of 30 where it's possible.)
Note that the low 2% conception chance is mitigated by looking at a failure rate over a full year, i.e. multiply 2% by the number of encounters in a year.
0.98 ^ 35 = 0.49, i.e. 51% chance of failure.
Failure here means child conceived. And keep in mind that there is only approximately a 2% chance of having a child from each encounter, so condoms fail a LOT. (20% chance of a child if done at the right time divided by 3 days out of 30 where it's possible.)
Note that the low 2% conception chance is mitigated by looking at a failure rate over a full year, i.e. multiply 2% by the number of encounters in a year.