弱【じゃく】

弱 goes straight after a number and its counter and means "just under": the real figure is a little below the round number you give. It works with time, distance, money, weight, people and percentages.

弱 covers the whole of number plus counter: に2じかん時間じゃく弱 is "a bit less than two hours". It goes on a round figure you are approximating, not on an exact count.

弱 and 強

On the Japanese earthquake scale, 弱 and 強 are fixed grades rather than approximations: しんど震度ご5じゃく弱 is "intensity 5-lower", a level of its own, and only 5 and 6 are split this way.