The total blood volume of a healthy person accounts for about 7% ~ 8% of the body weight, that is, the total blood volume of a person weighing 50 kg is about 4000 ml. Generally speaking, the total blood volume of an adult is about 4000 ~ 5000 ml. Usually, 80% blood circulates in the heart and blood vessels to maintain normal physiological functions; Another 20% of the blood is stored in the liver, spleen and other organs. Once blood loss or strenuous exercise occurs, blood will enter the blood circulation system.
A person who donates 200 ~ 400 ml blood at a time only accounts for 5% ~ 10% of the total blood volume, and the blood stored after blood donation will be replenished immediately without reducing the circulating blood volume. Water and inorganic substances lost after blood donation will be replenished within 1 ~ 2 hours; Plasma protein is synthesized by the liver and can be supplemented in a day or two; Platelets, white blood cells and red blood cells can also recover to their original levels quickly.
Human blood is constantly metabolized, many blood cells are aging and dying all the time, and at the same time, a large number of new cells are produced to maintain the balance of human metabolism. After blood donation, due to the enhancement of hematopoietic function, the lost blood cells were quickly replenished. Therefore, a healthy person who donates blood according to the regulations will not have any influence on his body, let alone "hurt his vitality", but will be beneficial to his body.
"For me, anything can become math." The mathematician Descartes once said this. "The universe is big, the particles are tiny, the speed of rockets, the cleverness of chemical engineering, the change of the earth, the complexity of daily use, and mathematics is everywhere." Hua, a famous mathematician in China, once reached such a conclusion. Indeed, as the two predecessors said, mathematics is closely related to our lives, and the footsteps of mathematics are everywhere.
2006 is coming to an end, and a new year -2007 is coming. Walking on the busy street, promotional signs of "400 for over 400" and "300 for over 300" can be seen everywhere. "This is really affordable!" Consumers flock to shopping malls, which are crowded with people, and snapping up is a common occurrence. This situation really makes people feel that they have returned to the era of material scarcity. In fact, the merchants have already laid their wishful thinking in their hearts. As the saying goes, only buy at a loss, don't sell at a loss, and the "400 yuan coupon for over 400 yuan" is just a sales promotion method for merchants, which hides mathematical problems, trade secrets and many mysteries.
Last year, our family of three also "shopped" in the shopping mall on the occasion of the Chinese New Year. At that time, more than 400 coupons were sent to 400 yuan. First, I bought my father an apple leather jacket with 980 yuan and sent a shopping voucher to 800 yuan. We didn't waste too much. We spent 298 yuan to buy a navy Li Ning cotton-padded jacket, and used 488 of the remaining 500 yuan coupons to buy a Taizilong men's suit (as it is a shopping voucher, no change). How much cheaper? 298+488+980= 1766 (yuan)-this is the money that needs to be spent when there is no discount. 980/ 1776, the discount is about 55%.
My aunt and uncle used to be in the clothing business, and I know something about the relationship between the purchase cost and the sales price of clothing. The purchase price of clothing generally only accounts for 20%~30% of the suggested retail price. With the intensification of competition and the promotion of shopping malls, in order to maintain profits, merchants or manufacturers continue to raise the suggested retail price of clothes. As a consumer who saw on TV a few days ago said, the suggested retail price of a pair of nylon trousers of the same style of a certain brand was only 299 yuan three years ago, and this year's price tag has become 999 yuan. Based on this calculation, the purchase price is only about 10%~20% of the market price. Even with a 55% discount, businesses can still earn 30% to 50% gross profit.
Advertising, advertising, advertising. Many people rush to buy and shop, and the flow of people in shopping malls increases, and the sales of goods also increase rapidly. Just when the flow of people is three times as usual, another math problem comes. Suppose a commodity is sold at a 20% discount when there is little traffic. 20% off the purchase price, 20% off the purchase price, and 6% of the marked price becomes gross profit. Although you may only earn 30% to 50% with 400 yuan coupons for the same product over 400, the sales volume is at least three times that of usual. Calculated by 30% gross profit and triple sales, 3×3=9, compared with the usual 60% gross profit, you can earn 50% more in one day. Although the gross profit margin of each product sold in this way has decreased, the gross profit has increased due to the increase of sales volume, and because of the large sales volume, the capital turnover has been accelerated and additional income has been brought.
There are mathematics in commodity pricing and promotion, mathematics in shopping consumption, mathematics in house decoration, mathematics in sweater weaving ... In short, mathematics is everywhere in real life!