Jim and Bob are maths students who both use Brilliant.Their rating increases by when they solve a problem with a rating higher than their own rating,where is their current rating and is the rating of the problem they solved.When they get a problem wrong, their rating decreases by if the rating of the problem solved wrongly is less than their current rating and their rating decreases by if the rating of the problem is more than their current rating. Both of their ratings in Algebra are .This morning,Jim solved a problem with a rating of .After that,he got a problem with a rating of wrong.When Bob found out that Jim's rating had increased,he immediately started doing problems on Brilliant.Bob got a problem with a rating of wrong.What is the minimum rating of the next problem he has to solve correctly if he only has time to solve one problem and he wants to beat Jim or make their ratings equal?
Assume that Brilliant ratings are rounded to the nearest integer.
Round your answer to the nearest integer.
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First,Jim solved a problem with rating 1 7 0 0 when his current rating is 1 6 0 0 ,so his rating increases by
( 2 5 1 7 0 0 − 1 6 0 0 ) 2 = ( 2 5 1 0 0 ) 2 = 4 2 = 1 6
Jim's rating is now 1 6 1 6 .Then, his rating drops by
( 2 5 1 5 9 1 − 1 6 1 6 ) 2 = ( 2 5 − 2 5 ) 2 = 1
So,Jim's rating is now 1 6 1 5 .When Bob got his first problem wrong,his rating drops by
( 2 5 1 5 0 0 − 1 6 0 0 ) 2 = ( 2 5 − 1 0 0 ) 2 = 4 2 = 1 6
Bob's rating is 1 6 0 0 − 1 6 = 1 5 8 4 .To beat Jim,Bob needs to increase his rating by 1 6 1 5 − 1 5 8 4 = 3 1 .Then,we can construct an inequality
( 2 5 P − 1 5 8 4 ) 2 ≥ 3 1
Taking the square root of both sides, we get
2 5 P − 1 5 8 4 ≥ 5 . 5 6 7 7 6 4 3 6 2 8 . . . . . .
Then,we multiply both sides by 25
P − 1 5 8 4 ≥ 1 3 9 . 1 9 4 1 0 9 0 7 . . . . . .
Adding 1584 to both sides,we get
P ≥ 1 7 2 3 . 1 9 4 1 0 9 0 7 . . . . . .
So our answer is 1 7 2 3 .