Initial Margin

NO.PZ2020020601000015 问题如下 A trar contacts a broker to enter into a futures contrato purchase 5,000 bushels of whefor 600 cents per bushel. The initimargin is US3,000, anthe maintenanmargin is US2,000. Unr whcircumstanis the trar requireto provi more margin? How mumar-gin is require Unr whcircumstances cUS500 withawn from the margin account? The trar is requireto provi more margin if more thUS1,000 is lost from the margin account. This will happen if the priof whefalls more th20 cents because variation margin will then have recethe margin balanmore th5,000 * 20 cents = US1,000. The trar is requireto bring the balanin the margin account up to the initimargin level of US3,000. US500 cwithawn from the margin account if the pririses 10 cents or more (5,000 * 610 cents = US30,500, whiis US500 more ththe requireinitimargin of US30,000). 题干中是Purchase futuresUnr whcircumstances cUS500 withawn from the margin account?的答案中的价格上涨10美分，应该是价格下降吧？US500 cwithawn from the margin account if the pririses 10 cents or more (5,000 * 610 cents = US30,500, whiis US500 more ththe requireinitimargin of US30,000).谢谢老师解答。

The trar is requireto provi more margin if more thUS1,000 is lost from the margin account.  This will happen if the priof whefalls more th20 cents because variation margin will then have recethe margin balanmore th5,000 * 20 cents = US1,000.  ——不是很理解，明明是持有futures to sell，是一个空头，为什么跌的时候还不挣钱。 而且wheat跌20cent，现货实际也只跌了1000，futures是保证金交易，保证金的变动应该远少于这1000才对。 就比如用股指期货交易，当合约亏很大时，期货的保证金变动是按比例算的；当保证金变动很大时，期货的合约变动就极其巨大了。 这道题不懂，盼复，谢谢。