Google search the BOM (Billings ovulation method, I think) way of getting boy or girl. All depends on timing.

The boy sperm (X) swims faster but dies faster as well. They are the sprinters and only live for 1 - 2 days.

The girl sperm (Y) swims slowly (crawling) and can live up to 5 days in the vagina.

Depending on the ovulation period of your wife, you can roughly time your sexual intercourse to ensure the boy or girl reaches the egg first.

If you plan to have girl, intercourse should be had 2-3 days before her ovulation. This will ensure all the X sperms swim and dies after a couple of days. The ones left are the Y sperms which can live for 3-5 days and they will impregnate the egg.

If you plan to have a boy, wait for ovulation day + 1 day then have your intercourse. This will ensure the egg is already produced and the first ones to get to it will be the X sperms which swims faster.

This was taught in the family planning course by the BOM advisors. I think you can find them in Assunta hospital in PJ. According to them, can be up to 80% accurate if assisted by them.

Not tested by me though.