Lesson: Introduction to Decimals

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Hi Brent

In the Manhattan Prep practice question my thought pattern was similar to what you have provided in your model answer. However, I can’t make sense of the final part;

"If 1.43b5 rounded to the nearest THOUSANDTH = 1.436, then b MUST equal 5
So, x must equal 1.4355, which means 10 - x MUST equal 8.5645
Since we can answer the target question with certainty, statement 2 is SUFFICIENT”

Why MUST B equal 5? Why can’t B equal 6,7,8 or 9?

TIA!
gmat-admin's picture

Hi Matt,

Question link: https://gmatclub.com/forum/in-the-number-1-4ab5-a-and-b-represent-single...

KEY POINT: 1.43b5 rounded to the nearest THOUSANDTH = 1.436

Let's examine some cases...

If b = 5, the number becomes 1.4355
When we round 1.4355 to the nearest THOUSANDTH, we get 1.436
This MEETS the given condition

If b = 6, the number becomes 1.4365
When we round 1.4365 to the nearest THOUSANDTH, we get 1.437
This does NOT meet the given condition

If b = 7, the number becomes 1.4375
When we round 1.4375 to the nearest THOUSANDTH, we get 1.438
This does NOT meet the given condition

If b = 8, the number becomes 1.4385
When we round 1.4385 to the nearest THOUSANDTH, we get 1.439
This does NOT meet the given condition

Etc.

So, it must be the case that b = 5

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