12 multiple-choice questions, progressively harder.
A prize pool of 500500500 dollars is split in the ratio 2:3:52 : 3 : 52:3:5. What is the largest share, in dollars?
Solution
Correct answer: D
The parts total 2+3+5=102 + 3 + 5 = 102+3+5=10, so 10k=50010k = 50010k=500 and k=50k = 50k=50. The largest share is the 555 term.
10k=500 ⟹ k=50,5k=25010k = 500 \implies k = 50, \quad 5k = 25010k=500⟹k=50,5k=250
The largest share is 250250250 dollars.
Two numbers are in the ratio 9:59 : 59:5 and differ by 282828. What is the smaller number?
Correct answer: A
The difference is 9k−5k=4k9k - 5k = 4k9k−5k=4k, so 4k=284k = 284k=28 and k=7k = 7k=7. The smaller number is the 555 term.
4k=28 ⟹ k=7,5k=354k = 28 \implies k = 7, \quad 5k = 354k=28⟹k=7,5k=35
The ratio of AAA to BBB is 2:32 : 32:3, and the ratio of BBB to CCC is 3:43 : 43:4. What is A:B:CA : B : CA:B:C?
The shared term BBB is 333 in both ratios, so they already agree and chain directly.
A:B:C=2:3:4A : B : C = 2 : 3 : 4A:B:C=2:3:4
A punch mixes juice to soda in the ratio 4:34 : 34:3. To use exactly 121212 cups of soda, how many cups of juice are needed?
Correct answer: B
Soda is the 333 term, so 3k=123k = 123k=12 and k=4k = 4k=4. Juice is the 444 term.
3k=12 ⟹ k=4,4k=163k = 12 \implies k = 4, \quad 4k = 163k=12⟹k=4,4k=16
You need 161616 cups of juice.
Two numbers in the ratio 5:85 : 85:8 have a sum of 919191. What is the larger number?
The parts total 5+8=135 + 8 = 135+8=13, so 13k=9113k = 9113k=91 and k=7k = 7k=7. The larger number is the 888 term.
13k=91 ⟹ k=7,8k=5613k = 91 \implies k = 7, \quad 8k = 5613k=91⟹k=7,8k=56
Continuing: red and green were 3:23 : 23:2; adding 101010 red made it 2:12 : 12:1, giving 3k+10=4k3k + 10 = 4k3k+10=4k. How many green marbles are there?
Solve 3k+10=4k3k + 10 = 4k3k+10=4k for kkk, then green is the 222 term.
k=10,2k=20k = 10, \quad 2k = 20k=10,2k=20
There are 202020 green marbles.
A field of sheep and goats has them in the ratio 7:37 : 37:3, with 404040 animals in all. How many goats are there?
The parts total 7+3=107 + 3 = 107+3=10, so 10k=4010k = 4010k=40 and k=4k = 4k=4. Goats is the 333 term.
10k=40 ⟹ k=4,3k=1210k = 40 \implies k = 4, \quad 3k = 1210k=40⟹k=4,3k=12
There are 121212 goats.
Three partners invest in the ratio 4:5:74 : 5 : 74:5:7, totaling 160016001600 dollars. How many dollars does the middle investor put in?
Correct answer: C
The parts total 4+5+7=164 + 5 + 7 = 164+5+7=16, so 16k=160016k = 160016k=1600 and k=100k = 100k=100. The middle investor is the 555 term.
16k=1600 ⟹ k=100,5k=50016k = 1600 \implies k = 100, \quad 5k = 50016k=1600⟹k=100,5k=500
The middle investor puts in 500500500 dollars.
The angles of a triangle are in the ratio 2:3:42 : 3 : 42:3:4. What is the largest angle, in degrees? (The three angles add to 180180180.)
The parts total 2+3+4=92 + 3 + 4 = 92+3+4=9, so 9k=1809k = 1809k=180 and k=20k = 20k=20. The largest angle is the 444 term.
9k=180 ⟹ k=20,4k=809k = 180 \implies k = 20, \quad 4k = 809k=180⟹k=20,4k=80
The largest angle is 808080 degrees.
In a parking lot, the ratio of cars to trucks is 8:38 : 38:3. There are 333333 trucks. How many cars are there?
Trucks is the 333 term, so 3k=333k = 333k=33 and k=11k = 11k=11. Cars is the 888 term.
3k=33 ⟹ k=11,8k=883k = 33 \implies k = 11, \quad 8k = 883k=33⟹k=11,8k=88
There are 888888 cars.
The ratio A:B=3:4A : B = 3 : 4A:B=3:4 and B:C=4:9B : C = 4 : 9B:C=4:9. If B=20B = 20B=20, what is CCC?
The shared term BBB is 444 in both, so A:B:C=3:4:9A : B : C = 3 : 4 : 9A:B:C=3:4:9. Then B=4k=20B = 4k = 20B=4k=20, so k=5k = 5k=5 and CCC is the 999 term.
4k=20 ⟹ k=5,9k=454k = 20 \implies k = 5, \quad 9k = 454k=20⟹k=5,9k=45
A school has students to teachers in the ratio 20:120 : 120:1. There are 560560560 students. How many teachers are there?
Students is the 202020 term, so 20k=56020k = 56020k=560 and k=28k = 28k=28. Teachers is the 111 term.
20k=560 ⟹ k=28,1k=2820k = 560 \implies k = 28, \quad 1k = 2820k=560⟹k=28,1k=28
There are 282828 teachers.
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