The survival rate of a kind of sapling is 90% through test, how many saplings should be planted at least in order to ensure that 450 trees are planted alive?
一种树苗经试验成活率是90%，为了保证种活450棵，至少应种多少棵树苗？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">450 / (9/10)</gadget>
<output>500</output>

<result>500</result>