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When to take reciprocal

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When to take reciprocal

by JGaynor » Sat Mar 27, 2010 9:12 am
Hey everyone, I am having trouble with knowing when to take the reciprocal...so I would greatly appreciate any insight....

A total of n trucks and cars are parked in a lot. If the number of cars is 1/4 the number of trucks, and 2/3 of the trucks are pickups, how many pickups, in terms of n, are parked in the lot?
Answer: 8/15n

A similar problem with taking the reciprocal is:

At a certain pizzeria, 1/8 of the pizzas sold in one week were mushroom and 1/3 of the remaining pizzas sold were pepperoni. If n of the pizzas sold were pepperoni, how many were mushroom?
Answer: 3/7n

Thank you!

Jason
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by eaakbari » Sat Mar 27, 2010 11:17 am
Hey

In the first question
T+C = n

C=T/4

Substituting C in eqn

You get T=4n/5

Now since 2/3T = P
P = 2/3 * 4n/5


which turns out as 8n/15
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by eaakbari » Sat Mar 27, 2010 11:19 am
As for the second question.

1/8 x = m

1/3 (1-1/8)x = p = n

(1*7)/(3*8) = n

1/8x = m = 3n/7
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