A seal ate 50 percent of the first 80 smelt it came across => \(\frac{50}{100} * 80\)

Let x be the remaining number of smelt the seal came across

Total number is smelt the seal ate is \(\frac{50}{100} * 80 + \frac{30}{100} * x\)

=> \(\frac{50}{100} * 80 + \frac{30}{100} * x = \frac{40}{100} * (80 + x)\)

=> \((50 * 80) + 30x = 40 * (80 + x)\)

=> \(4000 + 30x = 40x + 3200\)

=> \(10x = 4000 - 3200\)

=> \(x = 80\)

UPDATE :

At first I solved only for 'x' and chose option E but the question actually asks for the number of smelt the seal ate which is

\(\frac{50}{100}* 80 + \frac{30}{100}* 80 = 64\)

Hence

option D Thanks

EgmatQuantExpert for the correct solution

Important learning for meAfter solving the variables, do explicitly check what the question has asked for. Don't just stop after calculating the variables you have assumed and pick an answer.

_________________

If you like my post press kudos +1

New - RC Butler - 2 RC's everyday

Tag me in RC questions if you need help. Please provide your analysis of the question in the post along with the tag.