If the second digit - the units or ones digit - is 0 you leave it as it is.
If it is 1, 2, 3, 4 you replace it by 0.
If it is 6, 7, 8, 9 you replace it by 0 AND add 1 to the previous digit.
If it is 5 then you replace it by 0. If the previous digit is even you leave it as it is, if it is odd, you add one.
Many schools naively teach that you should always round up 5s. This introduces an upward bias and the above is based on the IEEE standard 754. For more, on rounding half to even, see the link.
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If you were told to round two digit numbers to the closest 100, you could round everything from 10-99 to the nearest 100, inclusive of 10 and 99. I.e all two-digit numbers round up to 100. This is because "to the nearest hundred" does not mean "up to 100, or down to zero", since "zero" is not in the "hundred's" catagory. i.e you can only round up to 100.This means you have 89 seperate two-digit number which will round up to 100.
Round the fourth digit: 1.001
0
There are 21 two-digit prime numbers.
u look at the first two numbers of the decimals. If it s five (like it is) look at the next digit. Round it to...... the next big number