问题 单项选择题

A、B两辆火车同时从甲、乙两站相对开出,两车相遇后继续前进,到达对方车站。已知A车在相遇后所用的时间比相遇前所用的时间少l小时36分钟,B车在相遇后所用的时间比相遇前所用的时间多用2小时,并知A车每小时比B车快10千米。则两车的速度分别为多少千米/小时()

A.30,40

B.40,50

C.25,35

D.50,60

答案

参考答案:B

解析:

设B车速度为x千米/小时,则A车速度为(x+10)千米/小时。列方程2x=(x+10)×,解得x=40千米/小时。所以两车速度分别为40千米/小时、50千米/小时。

选择题
单项选择题

"You are not here to tell me what to do. You are here to tell me why I have done what I have already decided to do," Montagu Norman, the Bank of England’s longest-serving governor (1920-1944), is reputed to have once told his economic adviser. Today, thankfully, central banks aim to be more transparent in their decision making, as well as more rational. But achieving either of these things is not always easy. With the most laudable of intentions, the Federal Reserve, America’s central bank, may be about to take a step that could backfire.

Unlike the Fed, many other central banks have long declared explicit inflation targets and then set interest rates to try to meet these. Some economists have argued that the Fed should do the same. With Alan Greenspan, the Fed’s much-respected chairman, due to retire next year-after a mere 18 years in the job-some Fed officials want to adopt a target, presumably to maintain the central bank’s credibility in the scary new post-Greenspan era. The Fed discussed such a target at its February meeting, according to minutes published this week. This sounds encouraging. However, the Fed is considering the idea just when some other central banks are beginning to question whether strict inflation targeting really works.

At present centra1 banks focus almost exclusively on consumer-price indices. On this measure Mr. Greenspan can boast that inflation remains under control. But some central bankers now argue that the prices of assets, such as houses and shares, should also somehow be taken into account. A broad price index for America which includes house prices is currently running at 5.5%, its fastest pace since 1982. Inflation has simply taken a different form.

Should central banks also try to curb increases in such asset prices Mr. Greenspan continues to insist that monetary policy should not be used to prick asset-price bubbles. Identifying bubbles is difficult, except in retrospect, he says, and interest rates are a blunt weapon: an increase big enough to halt rising prices could trigger a recession. It is better, he says, to wait for a housing or stockmarket bubble to burst and then to cushion the economy by cutting interest rates-as he did in 2001-2002.

And yet the risk is not just that asset prices can go swiftly into reverse. As with traditional inflation, surging asset prices also distort price signals and so can cause a misallocation of resources-encouraging too little saving, for example, or too much investment in housing. Surging house prices may therefore argue for higher interest rates than conventional inflation would demand. In other words, strict inflation targeting-the fad of the 1990s-is too crude.

It is implied in the fourth paragraph that Mr. Greenspan is skeptical of ()

A. the stipulation of anti-monopoly rules and regulations

B. the intervention by central banks in asset prices

C. the prevention of economic recession

D. the countdown by the Federal Reserve of new economic upheavals