Rounding and difficult nines
When rounding up 9's you have to be careful.
If you round a 9 to 10 think of it as adding 9+1
| 9 |
| +1 |
10 |
You put a zero in the first column and add 1 to the next.
Example 1
Round 43.299 to two decimal places.
You would answer this as follows:
43.299 round to two decimal places
43.29̲9 underline the digit (of 2nd decimal place)
43.29̲9 look next door
9 It's five or more so you raise the score (round up)
43.29 9 becomes 10
43.30 add 1 to the next column and put a zero in the last column.
Answer:
43.299 rounded to 2 D.P. =43.30
Example 2
Round 34.997 to two decimal places.
You would answer this as follows:
34.997 round to two decimal places
34.99̲7 underline the digit (of 2nd decimal place)
34.99̲7 look next door
7 It's five or more so you raise the score (round up)
34.99 9 becomes 10
34.99 But if you add 1 to the next column that becomes 10.
35.00 Add one to the next column.
Answer:
34.997 rounded to 2 D.P. =35.00
Example 3
Round £19.90 to the nearest £1.00
Answer as follows:
£19.90 rounded to the nearest unit of 1
19̲.90 underline the digit (units 1)
19̲.90 look next door
9 It's five or more so you raise the score (round up)
19 9 becomes 10
20 Add 1 to the next column and put a zero in the last column.
Answer:
£19.90 rounded to the nearest £1.00 is £20
Example 4
Round £99.98 to the nearest £1.00
£99.98 round to the nearest unit of 1
99̲.98 underline the digit (units 1)
99̲.98 look next door
9 It's five or more so raise the score (round up)
99 9 becomes 10
99 But if we add one to the next column that becomes 10
100 Add one to the next column.
Answer:
£99.98 to the nearest £1.00 is £100
Example 5
Round 5.9999 to 3 decimal places
Answer as follows:
Round 5.9999 to 3 D.P.
5.999̲9 underline the digit (3 D.P.)
5999̲9 look next door
9 It's five or more so you raise the score (round up)
5.999 9 becomes 10
5.999 but if you add one to the next column that becomes 10
6.000 now add one to the next column.
Answer:
5.9999 to 3 decimal places is 6.000
