This is a good question which falls in the medium-hard difficulty band of the spectrum. The best part about this question is it tests you on how well you know a very basic concept in Geometry
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Any angle whose measure is between 0 degree and 90 degree is called an acute angle.
A pair of angles which add up to 90 degrees, are called complementary angles.
So, if ∠A + ∠B = 90, then ∠A is the complement of ∠B and ∠B is the complement of ∠A.
For example, the complement of 60 degrees is 30 degrees.
Since the two acute angles are in the ratio of 5:4, we can assume their actual values to be 5k and 4k. Then, their respective complements will be (90 – 5k) and (90 – 4k).
It is said that the complement of ONE (of 5k and 4k) is twice as large as the complement of the OTHER. Now this is where a certain degree of caution needs to be exercised because there can be two cases.
Case 1: (90-5k) is twice of (90-4k).(90 – 5k ) = 2(90 – 4k) which on simplification yields k = 30. Then, 5k = 150 and 4k = 120. These are not acute angles. So, we will have to look at the next case now.
Case 2: (90-4k) is twice of (90-5k).(90 – 4k) = 2(90 – 5k) which on simplification yields k = 15 (which is half of what we got in the previous case). So, quite naturally, 5k = 75 and 4k = 60, which are definitely acute angles.
Therefore, the sum of the measures of the angles is 135. So, the correct answer option is C.
In problems like these where there is a use of a phrase like ‘ONE is twice of the OTHER’, it’s a clear clue that the order is not known and multiple cases have to be taken. So, if you took up the first case and ended up with values of 150 and 120 and feel like you have hit a dead end, it’s time to take a step back and read the question again to see if you missed a case and then work out the other case.
Hope that helps!
Arvind,
CrackVerbal Prep Team