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Solution
Suppose that x boys and x girls joined the club. Then, the new ratio of boys to
girls would be (3 + x) :( 5 + x), which you are told is 3:4, and 3+x/5+x =3/4 ⇒ 4(3 + x) =
3(5 + x) ⇒12 + 4x = 15 + 3x x = 3. Therefore, 3 boys and 3 girls joined the
existing 3 boys and 5 girls, for a total of 14 members. The correct answer is B.

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Solution
Clearly, the more workers there are, the less time will be required, so used
multiplication. The jib takes: (15 workers) × (24 days) = 360 worker-days. Then
(40 workers) × (d days) = 360 worker-days. 40x = 360 d = 9 days. This can
also be set up as follows:360 worker-days/ 40workers = 9 days.

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Solution
We are told that has enough pills to last for 10 × 14 = 140 patient-days:
140 patient-days = (10 patients) × (14 days).
140 patient-days = (20 patients) × (7 days).
140 patient-days = (70 patients) × (2 days).
To solve this question, write: 140 patient-days = (35 patients) × (d days) ⇒d = 140/35 = 4.

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Solution
Handle the rate of the problem exactly like a ratio problem. Set up a proportion
and cross-multiply: pages/ minutes=24/15 = x/40 ⇒15x = 40 × 24 = 960 ⇒x = 64.

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Solution
Assume that the sides of the first square were 1 inch long, so that the area was 1 square inch. Then, the sides of the second square were 3 inch long, and it area was 9 square inches, an increase of 8 square inches or 800%.