百度百科

• 一(one; chief)ASSOCIATIVE
• 白(white; bright; clear)PHONO-SEMANTIC

A hundred is the leading number, shining brightly like pure white light.

• 广(roof; broad eaves)RADICAL
• 廿(twenty; many times measure)ASSOCIATIVE
• 又(right hand; again; once more)ASSOCIATIVE

Under a roof, use your hand to measure back and forth many times to get accuracy.

• 禾(rice plant)RADICAL
• 斗(threshing floor; rice threshing area)ASSOCIATIVE

To classify rice grain by measuring each type with a measuring vessel.