The smaller triangle has a side of 16, while the corresponding side for the larger triangle is 64.
The ratio of the two sides (small to large) is 16:64 which reduces to 1:4 after we divide both parts by 16.
The ratio 1:4 basically means "multiply the smaller length by 4 to get the larger length". In other words, the larger length is 4 times longer.
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From here, we square both parts of the ratio above
we go from 1:4 to 1:16 after we square both parts
What does the ratio 1:16 mean? It means that the larger area is 16 times that of the smaller area
If
x = smaller area
y = larger area
then,
y = 16*x
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We're told that the larger area is 1360 square cm. So we know that y = 1360. Use this to find x
y = 16*x
1360 = 16*x
1360/16 = 16*x/16
85 = x
x = 85
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Answer: The smaller area is 85 square cm
Answer is choice D