There are 99 boys and 1 girl are in a lecture theatre.how many boys must leave the theatre so that the percent of boys become 98 percent?

Well, if there are 99 boys and 1 girl, that's a total of 100 people. To have boys make up 98% of the group, you'd need 98 boys out of every 100 people. So, if you want boys to be 98% of the group, you'd need all the girls to leave the theatre.