Home › Community › Questions & Answers › Mental Math Q & A › I do not clearly understand Rounding Up

- This topic has 4 replies, 3 voices, and was last updated July 8, 2017 at 10:54 am by ImranOfpad.

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- July 8, 2017 at 10:54 am #5149
Would you please do for me a math step by step?Like this one 7423

Do not clear understand about last digits add up to 10.

all the other digits will add up to 9.

July 8, 2017 at 10:56 am #5151So say we want to round 7423 up to 10,000. The amount you rounded up by is 2577. Below is the breakdown of the steps.

7 + 2 = 9

4 + 5 = 9

2 + 7 = 9

3 + 7 = 10

The first digits in the above addition 7,4,2,3 are the digits of the original number (7423).

The second digits in the above addition 2,5,7,7 is the amount you have rounded up by (2577).

If instead you want to round up to 8000 instead of 10,000 you dont do the first addition. (7+2 =9). So the amount you rounded up by will be 577 (the last three digits of 2577 when we rounded up to 10.000)

Please let me know if this clarifies.

July 8, 2017 at 10:57 am #5154Thank you so much for this helpful reply. But i have a question , 10,000-7423 = 2577 every one knows.After figure out the answer,

- 7 + 2 = 9
- 4 + 5 = 9
- 2 + 7 = 9
- 3 + 7 = 10

why need this above calculation ?

Please don’t mind my question. I am actually not find out it’s important.

July 8, 2017 at 10:58 am #5156I showed you the calculation step by step just for your understanding. If you do 10,000 – 7423, then you are explicitly calculating the numbers.

If you know that the last digit adds up to 10 and the other digits add up to 9 you will be able to tell the rounded up value without calculating anything. So you can immediately see the number 7423 and say rounded up number is 2577 without doing any calculation.

Hope this clarifies. Let me know if I understood your question correctly and answered it.

July 8, 2017 at 10:59 am #5158Thank you so much for your clarification. Now i am completely understand the main point. And yes this technique is really helpful!!

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