Ntxiv yog qhov kev lag luam tseem ceeb. Ntxiv yog tus naj npawb ntawm ntau tshaj ob, pes tsawg tus synthesis, qhov no hu ua thiab. Sib ntxiv thiab sib rho, sib npaug, ntxiv rau tag nrho "plaub kev ua haujlwm".
Lub cim uas tshaj tawm hais ntxiv yog qhov kos npe ntxiv (+). Thaum sib ntxiv qhov ntxiv, cov khoom txuas nrog ib qho ntxiv rau. Thiab muab qhov sib npaug sib npaug (=) tom qab.
Piv txwv: 1, 2 thiab 4 thiab tus lej 7, sau raws li: 1+2 +4=7.
