these percentages varied by age, and were at their highest for those aged 3 to 15 and at their lowest for those aged 16 to 29
roedd y cyfrannau hyn yn amrywio yn ôl oedran, ac ar ei huchaf ar gyfer y rhai 3 i 15 oed ac ar ei hisaf ar gyfer y rhai 16 i 29 oed