We all know that multiplication tables are very important for doing most of our calculations. And we have learned tables up to 10, but what about the teen numbers? Today we are going to learn an easy method to multiply numbers between 11 and 19 among themselves mentally without using paper or pen.
Example: 16 x 12
1. Add 16 + 2 (the units digit of 12) = 18
2. Add a zero, or multiply by 10 = 180
3. Multiply the units digits of the given numbers: 6x2 = 12
4. Add 180 + 12 = 192. This is the answer.
1 6
1 2
(16 + 2) x 10 6 x 2
180 + 12
The answer is 192
Example: 19 x 17
1 9
1 7
(19 + 7) x 10 9 x 7
260 + 63
The answer is 323
Some more practice
a) 14 x 12 = (14 + 2) x 10 = 160 + (4 x 2) = 160 + 8 = 168
b) 16 x 13 = (16 + 3) x 10 = 190 + (6 x 3) = 190 + 18 = 208
c) 15 x 18 = (15 + 8) x 10 = 230 + (5 x 8) = 230 + 40 = 270
Try these:
1) 12 x 15
2) 13 x 18
3) 16 x 19
4) 15 x 14
5) 17 x 11
Famous Mathematicians.
Pythagoras
Pythagoras of Samos (570 BC – 495 BC) was a Greek philosopher, mathematician, and founder of the religious movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is available about him.
He was born on the island of Samos, and may have travelled widely in his youth, visiting Egypt and other places, seeking knowledge. He spent most of his life in the Greek colonies in Sicily and southern Italy. He had a group of followers who followed him around and taught other people what he had taught them. They wore their hair long, and wore only simple clothing, and went barefoot. Pythagoreans were interested in philosophy, but especially in music and mathematics, two ways of making order out of chaos. Music is noise that makes sense, and mathematics is rules for how the world works.
He is revered as a great mathematician, mystic and scientist, but he is best known for the Pythagorean Theorem that bears his name. He worked on the theory of numbers and had knowledge about drawing figures such as pyramids and cubes. He advocated that the circle was the most perfect path and led his followers to believe that the sun was at the centre of the Universe and the paths of the planets were circular.
The Pythagorean Theorem states that in a right-angled triangle the area of the square on the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides — that is,
