Fraction Problem

[me.prasanna]

Q.) Miguel is mixing up a salad dressing. Regardless of the number of servings, the recipe requires that 5/8 of the finished dressing mix be olive oil, 1/4 vinegar, and the remainder an even mixture of salt, pepper and sugar. If Miguel accidentally doubles the vinegar and forgets the sugar altogether, what proportion of the botched dressing will be olive oil?

A 15/29
B 5/8
C 5/16
D 1/2
E 13/27

Solution : When I look at the solution provided by the MGMAT, it works. But here is my approach:

Since Vinegar is originally 1/4, after doubling it, it would become 1/4.

So now if we sum up everything it should be:

Olive Oil + 1/2 ( Vinegar) + 1/24 ( Salt) + 1/24 Pepper = 1

Olive Oil = 1 - (1/2+1/24+1/24)

Olive Oil = 10/24

Can someone please correct my mistake ?

Thanks
Prasanna

[JonathanSchneider]

Doubling the AMOUNT is not the same as doubling the PERCENTAGE.

Think of it this way. Let's say you're making a sandwich. You like your sandwich to be 1/2 peanut butter and 1/2 jelly. If you double the amount of peanut butter, do you have 100% peanut butter? Of course not. You just have a higher % peanut butter than before.

The easiest route for a problem such as this is to pick some real numbers from the outset. Then double the real number you've picked for the AMOUNT of vinegar, and reinsert that into the total to see what new fraction results.