Lesson 26. Rounding numbers

воскресенье, 12 февраля 2017 г.

Lesson 26. Rounding numbers

Rounding off numbers.

1. Rounding to the nearest whole number.

If the first digit after the decimal point is 5 or more round up. Otherwise round down.

2. Rounding to the nearest 100.

If the first digit in the tens column is 5 or more round up. Otherwise round down.

Decimal places.

Rounding off to 1 decimal place.

If the figure in the 2^nd decimal place is 5 or more, round up. Otherwise do not.

Significant figures.

For significant figures we approach from the left and start counting as soon as we come to the first figure which is not zero. Once we have started counting, we count any figure, zeros included.

EXAMPLE:

Round 63.8251 to 3 significant figures (3 s. f.)

(Count 3 figures. The ‘next’ figure is 2 which is less that 5 so do not round up.)

63.8251 = 63.8 (to 3 s. f.)

EXAMPLE:

Round 8.0374 to 3 s. f.

(Count 3 figures. The ‘next’ figure is 7 which is more that 5 so round up.)

8.0374 = 8.04 (to 3 s. f.)

EXAMPLE:

0.0654516 = 0.0655 (to 3 s. f.)

EXAMPLE:

Notice that we need the two noughts after the ‘4’ as the original number 6382.7 is approximately 6400 not just 64.

EXAMPLE:

Now can you round 37,923 to the nearest thousand?

Look at the digit to the right of the rounding digit. If it is 5 or greater, add 1 to the rounding digit. If it is less that 5, leave the digit alone.

37,923

9 is greater than 5. Add 1 to the digit 7. Change the digits to the right to zeros.

38,000

37,923 rounded to the nearest thousand is 38,000

EXAMPLE:

Now can you round 621,344 to the nearest hundred?

Look at the digit to the right of the rounding digit. 4 is less than 5.

621,344

Leave the rounding digit alone. Change the digits to the right to zeros.

621,300

621,344 rounded to the nearest thousand is

621,300

Tasks to the lesson 26

Other lessons:

Уроки математики и физики для школьников и родителей

воскресенье, 12 февраля 2017 г.