Taking a math test can be pretty stressful. Even if you know the material, you can still get the problem wrong. Knowing how to go through your math test and check your work can save you from handing in a test full of mistakes that can be avoided. {#blank#}1{#/blank#}

Write it out

    You can also check a math problem by writing everything out on paper. {#blank#}2{#/blank#} Writing out math problems reduces your chances of missing anything to the lowest possible level, which is a common cause of incorrect answers.

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    Make sure your answers work by doing the opposite procedure of what your problem calls for, including the answer you got the first time around. In other words, you would use the opposite of this addition problem—subtraction (减法)—to determine whether or not your answer is the correct one.

Plugging in

    You may find that a variable isn't good enough or have a problem where you have to solve for a variable (变量). {#blank#}4{#/blank#} This is the only real way to assure yourself that the answer you've found is correct.

Check for a reasonable answer

    {#blank#}5{#/blank#} For example, if you get an answer in the millions and you know it should be in the thousands, you've likely misplaced a point. Go back through the work on your paper to make sure all of your formulas and calculations are correct. If everything looks okay, do the problem again and compare the result of the second try to what you've got on the first try.

    Since my family were not going to be helpful about my taking a cooking job, I decided I would look for one all by myself and not to tell them about it till I'd got a permanent one.

    I had seen an agency advertised in a local paper, so as soon as there was no one about to say “Where are you going?” I rushed out of the house in search of it. I was wildly excited, and as nervous as if I were going on the stage. Finding the place quite easily, I tore up three flights of stairs, and swung breathlessly through a door which said “Enter without knocking, if you please.”

    The simple atmosphere of the office calmed me, and I sat down on the edge of a chair. The woman at the desk opposite looked carefully at me. Then she questioned me in a low voice. I answered softly and started to feel helpless. She wondered why I was looking for this sort of job, so I felt I had to give her the idea of a widowed mother struggling against poverty. But I felt more helpless when she told me that it would be difficult to get a job without experience or references. Suddenly, the telephone on her desk rang. While having a mysterious conversation, she kept looking at me. Then I heard her say:

    “In fact, I've got someone here who might suit.” She wrote down a number, and my spirits rose as she held out the paper to me, saying: “Ring up this lady. She wants a cook immediately. Cook a dinner for ten people tomorrow. Could you manage that, I wonder?”

    “Oh, yes,” say I—never having cooked for more than four. Then I rushed out and called the lady, Miss Cathy. I said confidently that I was just what she was looking for. “Are you sure?” she kept saying. Anyway she decided to employ me and a permanent position if I carried out the promise of my self-praise. I asked her what tomorrow's menu was to be.

    “Just a small, simple dinner: lobster cocktail, soup, turbot mornay, fruit salad and a savory.” In a rather shaken voice I promised to turn up in good time tomorrow and rang off.

    New York's iconic, blue-green statue of liberty wasn't always green. When the statue was gifted to the US from France in 1885, she was actually a shiny copper color. A new video reveals the chemical reactions involving oxygen and even air pollution that led to her color change from copper to liberty green. The statue of liberty was a gift from France to the US as a way of commemorating the US's fight for independence, as well as their own aspiration for democracy.

    A video, published by the American Chemical Society, explains that the 305-foot (93 meter) statue was built over nine years in sections of copper skin on top of an iron skeleton.

    In her first few decades in the Big Apple, the statue slowly turned from that shiny copper color to a dull brown and the, finally, to the blue-green, or as they'd say back in France, 'verdigris' we see today,' said the video's narrator.

When it changed color, some officials suggested restoring her back to her original color, but after the public protested against this decision, she was left the way she is. The statue's color change was as a result of oxidation reactions between copper and the air. But it was more than one reaction - the color change is due to about 30 years worth of different reactions leading to a mixture of greenish minerals.

    Oxidation reactions happen when an atom loses an electron to another atom.

    In the case of the statue of liberty, her color change was bound to happen due to oxygen in the atmosphere that is 'hungry' for electrons. On top of this, elements of New York City's polluted air added to the color change too.

The first chemical reaction of the color change involved copper giving up electrons to electron-hungry oxygen in the atmosphere. This led to a mineral called cuprite - which is pinkish red.

    Then, cuprite loses even more electrons to oxygen, forming a new mineral（矿物质） called tenorite, which is blackish in color. The black color of tenorite explains why the statue got darker over time, forming a dark brown color.

    Then, further chemical reactions occurred when sulfur（硫） in the atmosphere reacts with oxygen to form sulfur dioxide. Sulfur comes from natural processes such as volcanic eruptions, but also from man-made emissions from boats, cars, airplanes and factories. When sulfur dioxide in the atmosphere reacts with water, it produces sulfuric acid. Sulfuric acid forms green minerals with copper oxides, so the sulfuric acid in the atmosphere made the state green over time.

    Added to that, chloride from the sea spray surrounding Ellis Island where the statue is located made the statue even greener.

    The statue stayed this way for over 100 years because the exposed copper is now oxidized and stable, but the statue wouldn't be the same anywhere else.

A Letter that Changed My Life

    I was about 30 years old and was working as a firefighter in the South Bronx's Engine Co. 82. It was a restful Sunday and between alarms I rushed to the office to read a copy of the New York Times. I read an article on the Book Review section which openly stated what I took to be a calumny – that William Butler Yeats had gone beyond his Irishness and was forever to be known as a universal poet. As I read it, my blood began to boil.

    There were few things I was more proud of than my Irish heritage, and ever since I first picked up a book of his poems from a shelf when I was in the military, Yeats had been my favorite Irish writer, followed by Sean O'Casey and James Joyce.

    I grabbed a piece of paper and wrote out a letter of anger to the editor. Throughout Yeats' poetry, his view of the world and the people in it was basically Irish. He had lived his life and written his poetry through the very essence of his Irish sensibility. It was offensive to think Irishness was something to be transcended(超越).

    I don't know why I felt it my duty to safeguard the reputation of the world's greatest poet. I just knew that I had to write that letter.

    After my letter got published, I received a letter from The New Yorker, asking for an interview. When my article Fireman Smith appeared in that magazine, the editor of a large publishing firm called me, asking if I was interested in writing a book about my life. I had little confidence to write a whole book, though the subject was worthy. I wrote Report From Engine Co. 82 in six months, and it sold really well. In the years that followed, I wrote three more best-sellers.

    Being a writer had been far from my expectations. How had it happened? I often found myself thinking about it, and my thoughts always came back to that letter to the New York Times. For me, the writing was a natural consequence of the passion I felt and the subjects represented the great values burning within me as I wrote.

    Over the years, my five children have come to me with one dilemma or another. My answer is always the same. Think about what you're feeling and measure the heat of the fire in your heart, for that is your passion. Your education and your experience will guide you toward making a right decision, but your passion will enable you to make a difference in whatever you do. That's what I learned the day I stood up for Ireland's greatest poet.

Ida Nelson and her sister were relaxing and enjoying themselves in the sauna (桑拿室) when she heard a series of long low sounds from a small airplane circling the nearby airport.

It was 11:30 at night in the Alaskan village of Igiugig, population 70, and, as she told the reporter, "Any time a plane flies over that late, you know something is wrong."

Nelson and her sister leaped out of the sauna, ran to the window, and saw the problem: The airport's runway lights were out.

Nelson threw on some clothes, jumped into her ATV, and floored it to the airport, where she found a local pilot trying to turn on the lights manually.

"Normally, if you push the button 10 or 15 times, the lights will just light up," Nelson told KTOO out of Juneau. Not this time. Meanwhile, she and the pilot learned of the plane's urgent mission: It was a medevac (医疗救护直升机), there to transport a seriously ill local girl to the nearest hospital, 280 miles away in Anchorage.

Nelson had a plan. Driving her ATV to the end of the runway, she shone her headlights for the plane to follow. Great idea, but it wasn't enough. More light was needed, so a neighbor called nearly every home in the village—32 of them.

Within 20 minutes, 20 vehicles arrived at the airport, many of the drivers still in pajamas (睡衣). Following directions from the medevac pilot, the cars lined up on one side of the runway.

The medevac made its final approach and, guided by the headlights, landed safely. The young patient was loaded onto the aircraft, and the plane immediately took off again. Her illness was never publicly revealed, but she has since been released from the hospital.

In a world filled with uncertainty, the little community's positive activism was a big deal. Not so much for Nelson. As she told the reporter, in Igiugig, coming together "is kind of a normal deal."