Life will become easier with 9 quick calculation tips learned from elementary school

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Math has a lot of quick mental arithmetic tips , interesting rules that are easy to apply in life, and help arouse your computational passion. A number of very useful and simple daily calculation tips that can be calculated by hand. However, over time, they are somehow forgotten and are now called the " grandma's tips ".

On the Bright Side page, I decided to recall 9 quick calculation tips that I learned from elementary school , which most of us forget, make life easier. Invite you to consult!

Determine the time remaining before the sun sets

Since time immemorial, when there is no watch or mobile phone to see the time, people often observe the Sun to estimate the time of day. But the special thing here is that you just need to use your hand to determine the time when the Sun goes down .

Just close your hand and bring it to the Sun so that the edge of your index finger touches the Sun, the other fingers overlap with the horizon ( as shown above ). Count the number of fingers from the Sun to the horizon, each of your fingers now representing 15 minutes before night falls.

Calculate the number of days in a month

Hold your hand and start counting months according to the joints. Each joint emerges or the distance between two joints is counted as one month. If only counting on one hand, after the turn is over, start again at the joint of the index finger of the other hand.

The month on the floating joint is 31 days, and the distance between the two joints is 30 days or less .

Determine whether the Moon is missing or round

This may sound a bit confusing, but the reality is very simple. In order to teach your child how to determine the phases of the Moon, remember 3 letters: D; O and C. The word D is in the rounding phase; The letter O is a full moon and the letter C indicates that the Moon is in a phase of gradual defect.

Tips to remember Roman numerals

In middle school, it seems that we only remember Roman numerals I, V, X corresponding to numbers 1, 5, 10, right? But now you are confident that you know the Roman numerals hundreds and thousands.

To remember Roman numerals, you can use this phrase: " Мy Dear Сat Loves Хtra Vitamins Intensely " in English. The capital letters represent Roman numerals in descending order: M (1000), D (500), C (100), L (50), X (10), V (5), I (1).

Check battery quality

It's easy to quickly check if the battery is still usable ; or a new battery or battery is running out of power when there is no voltmeter, by putting two batteries high, about 1-2cm above the table and then dropping it lightly. New alkaline batteries will not bounce and stand firmly on the floor , indicating that the battery is full and usable.

Which battery has less electricity, it will bounce like a spring and emit a hollow sound ( like when you drop a light object on the floor ), bouncing several times and eventually falling, it is a dry battery, or battery dead . You can basically understand that the battery is dead or the battery is dead, the amount of alkali is only a little left, mostly gas, so it will be light and unstable when you drop it on the table.

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Multiply the numbers 6, 7, 8, 9 by using your fingers

This method is called " Russian Multiplication " to perform multiplying numbers 6 through 9 without the multiplication table. First of all, you need to number the fingers on your hands as shown, the pinkie is 6 and the thumb is 10.

For example, when you want to perform a 7 x 8 calculation, touch two fingers with the corresponding numbers 7 and 8 in your hands.

After that, the total number of fingers below ( including two fingers touching each other ) is dozens . In this calculation, the number of fingers below is 5 so tens is 5 (or 50). The number of fingers above is the unit row ( in the picture is 3 x 2 = 6 ). Finally, join the number of tens with the ones unit resulting in 56. Therefore, calculation 7 x 8 = 56.

With this mental arithmetic, you can quickly calculate the product of 6, 7 and 8.

To make multiplication with 9 , straighten your fingers out, put your hands face down on the table. Now, multiply any number by 9 and just bend the finger corresponding to that number. The fingers on the ' front ' of the corresponding finger are dozens, the next finger is the unit.

For example, 7 times 9, you just need to bend your 7 finger up, 6 fingers left " front " corresponding to the tens digit 6 ( or 60 ) and 3 fingers left " back " with 3 units. We get 7 x 9 = 63.

Measure the distance by hand

If you need to measure the length of something but don't have a ruler or any tool you can use, you can use your fingers. Corresponding to the average human size, the distance between the thumb and index finger is 18cm; The distance between the thumb and the little finger is 20cm . Of course, this method is not 100% accurate because each of our hands has a different size. However, it will be useful in case you need to measure a large object with a small ruler: just measuring that distance with your fingers is okay.

Measure the size of an angle

Spread your fingers wide, as wide as possible and place your hand on a flat surface, up on the corner you want to measure.Your little finger is 0 °. The angle between the thumb and the little finger is 90 °, the angle between the little finger and the other finger is 30 °, 45 ° and 60 °, respectively.

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Having fun!