SOLUTION: The time necessary T to make an enlargement of a photo negative varies directly as the area of the enlargement. If 108 seconds are required to make a 3-by-4 inch enlargement, find

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Question 22890: The time necessary T to make an enlargement of a photo negative varies directly as the area of the enlargement. If 108 seconds are required to make a 3-by-4 inch enlargement, find the time required to make a 6-by-8 inch enlargement.
A. 384 seconds
B. 528 seconds
C. 480 seconds
D. 432 seconds
Answer by rapaljer(4551) (Show Source):
You can put this solution on YOUR website!
Step 1: Write an equation relating the variables using k for a constant:
T=kA

Step 2: Substitute one complete set of variables and solve for k:
T=kA
108 = k*12

Divide by 12:

Step 3: Use this value of k to answer the question about T.
The question is to find T when A= 6*8 = 48:
T=9A
T= 9*48
T= 432 seconds, which would be D.

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