The time $T$ necessary to make an enlargement of a photo negative varies directly as the area $A$ of the enlargement. If 245 seconds are required to make a 5 - by- 7 in. enlargement, find the time required for a 7 - by- 10 in. enlargement.
A) 560 seconds
B) 630 seconds
C) 420 seconds
D) 490 seconds

Question

Quizplus · Accepted Answer

The area of the 5-by-7 enlargement is $35$ square inches, and the area of the 7-by-10 enlargement is $70$ square inches. Since time varies directly with area, the ratio of the times is equal to the ratio of the areas: $\frac{T_2}{245} = \frac{70}{35}$. Solving for $T_2$, we get $T_2 = 490$ seconds.

The Time TTT Necessary to Make an Enlargement of a Photo Negative Varies

The Time $T$ Necessary to Make an Enlargement of a Photo Negative Varies