- Know the places for each unit. (ones, tens, hundreds…tenths, hundredths, thousandths…)
- If the digit to the right of the place value you want to round is 5 or more, round up; if it is 4 or less, round down.
- Example: Round 475 to the nearest 10. The
- The number to the right of the 10’s place is 5 or more, so round up by adding 1 to the 10’s place. 475 à 480

- When adding or subtracting decimals, make sure to line up the decimal points.
- When multiplying decimals, do the problem as though the decimal numbers were whole numbers. Then, add up the total number of places to the right of the decimals in the two factors. This gives the number of decimal places in your answer.

- First multiply the numerators, then multiply the denominators.
- Example: 3/5 x 6/13 = 3 * 6/5 * 13 = 18/65

- Find the reciprocal of the divisor.
- Multiply the reciprocal and the dividend to get the quotient.
- Example: 4/5 divided by 3/7 = 4/5 * 7/3 = 4 * 7 / 5 * 3 = 28/15 = 1-13/15

- Find the common denominator
- Rewrite all fractions using the common denominator
- Add the numerators and put the total over the common denominator
- Example ½ + 4/10 + 4/5
- Common denominator = 10
- 5/10 + 4/10 + 8/10 = 17/10 = 1-7/10

- What is 20% of 95? (In math, of means times)
- x = 20% * 95
- Rewrite the percentage as a decimal
- x = .20 * 95
- x = 19

- 30% = 30/100 = 0.30
Percent means “per 100” or “out of 100.”

So, 30 percent means 30 out of 100, or 30/100Decimal places to the RIGHT of the decimal are, in order, tenths, hundredths, thousandths, and so on.

So, 30/100, or 30 hundredths means you put a 30 in the hundredths place.

DECIMAL TENTHS HUNDREDTHS THOUSANDTHS

. 0 30 0

Since 30 is too large to fit in the hundredths place by itself (2 digits) we put the overflow into the next larger spot – the tenths place and leave the 0 in the hundredths place. Here the number 30 means 3 of the next larger decimal. Just like when you are counting, when you get to 9 you put a 1 in the tens place and put the 0 in the ones place. Here, we do the similar thing which gives us:

0.30

If we had 34%, that would be 34/100 and we would put 34 in the hundredths place. Again, since we can’t put 2 digits into the hundredths place, we move the overflow into the tenths place (again, this time it’s the 3) and leave the 4 in the hundredths place which leaves us with:

0.34

- Total all the numbers
- Divide by the number of numbers
- Example 6, 9, 13, 19, 23 (5 numbers)
- Find the sum – 6+9+13+19+23 = 70
- Divide the sum by the number of numbers -- 70/5 = 14
- The mean is 14