Misra’s blog

Math

Posted by mtwinkle on June 11, 2007

PEMDAS

How to recognize multiples of:

2 – Last digit is even

3 – Sum of digits are multiple of 3

4 – last two digits are multiple of 4

5 – Last digit is 5 or 0

6 – multiple of 2 & 3

9 – Sum of digits is a multiple of 9

10 – last digit is 0

12 – multiple of 3 & 4

The average of evenly spaced numbers is simply the average of the smallest number and the largest number.

eg. The average of all the integers from 13 to 77, is the same as the average of 13 and 77.

(13 + 77) /2 = 45

What is the sum of the integers from 10 to 50, inclusive?

Average= (a+b)/2 =  30

Number of terms = (a-b+1) =41

Sum = avg * number of terms = 30 * 41

Median – Put the numbers in numerical order and then

odd – The middle number

even – The average of the two numbers in the middle

Mode – The number that appears more often.

Range – The positive difference between the highest and the lowest values

Area of a triangle = 1/2 * base * height

Isosceles triangle = Has 2 equal sides and 2 equal angles

Equilateral triangles – 3 equal sides and 3 equal angles (60 degrees)

Similar triangles – corresponding angles are equal and corresponding sides are proportional.

Right angle triangle – a2 + b2 = c2

area of a parallelogram = base * height

area of trapezoid = (avg of parallel sides) * height

circumference of a circle = 2 pi r

area of a circle = pi r * r

slope of a line =  (change in y)/ (change in x)

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