A precision measurement of the branching ratio K{sup +} {r_arrow} {pi}{sup +}{pi}{sup 0}/K{sup +} {r_arrow} {mu}{sup +}{nu}{sub {mu}}

A measurement of the branching ratio K{sup +} {r_arrow} {pi}{sup +}{pi}{sup 0}/K{sup +} {r_arrow} {mu}{sup +}{nu}{sub {mu}} was made using stopped kaons from p{anti p} annihilations at rest and a magnetic spectrometer to measure the momenta of the charged decay product to the 1% to 1.5% level. The determination is based on 45,500 events passing final data cuts. The resulting ratio is .3329 {+-} .0047 (statistical) {+-} .0010 (systematic).