Bunuel wrote:

A health food store prepares a breakfast food that consists of oats, raisins, and nuts mixed in the ratio 9:2:1, respectively, by weight. If the nuts in the mixture weigh 9.2 pounds, how many pounds does the total mixture weigh?

(A) 82.2

(B) 92.2

(C) 101. 2

(D) 110.4

(E) 165.6

O:R:N=9:2:1 = O:R:9.2 = 9x:2x:x

so if x is 9.2, (9+2+1) x or \(12x = 9.2*12\)

Ofcourse the question now is all about doing fast calculations.

Choices can help as answer is NOT approximate but exact

ways this can be done faster

1)

TENTHs/last digit - last digit of the product will be 2*2 = 4

Only D has a 4

2)

DIVISIBILITY by 4 and 3 9.2 is not a multiple of 3 but 12 is multiple of 3

so the product 9.2*12 should be a multiple of 3 and 4 but not of 9

(A) 82.2... last two digits are 22 : not div by 4

(B) 92.2 ... 9+2+2=13 : not div by 3

(C) 101. 2.. 1+1+2=4 : not div by 3

(D) 110.4... 1+1+4 = 6 : div by 3 .. and 04 is div by 4.. HENCE our answer

(E) 165.6 ... 1+6+5+6=18: Div by 3 but also by 9

D

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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