Tip #39 to Get a Top SAT Math Score
There is a complex formula for sequence questions that you may or may not have used in school, but on the SAT we do not need it. There are only two kinds of sequence questions on the SAT (Skills 39 and 40). The first requires you to write out a bunch of terms and do something with them, such as find the sum or average.
Solution: Write out the first 5 terms of the sequence, following the directions: 3, 7, 11, 15, 19. Then find the sum by adding these five terms.
That was so easy to explain that I have some room left. So, here's Brian's Math Magic Trick #2.
- 3, 6, 12, 24, …
- In the sequence above, the first term is 3 and every number after that is found by doubling the preceding number. What is the 7th term in the sequence?
- 112, 54, 18, …
- In the sequence above, each number after the first is of the preceding term. What is the 6th term of the sequence?
- What is the greatest of four consecutive prime integers, if the least is integer is 11 ?
- The first term in a sequence is 12, and the second term is 8. The third term and each term after the third are the average of the preceding two terms. What is the value of the first term in the sequence that is an odd number?
- In a given sequence, the first term is 1, and every number after the first is found by adding 3 and then doubling the result. What is average of the first six terms in the sequence?
- Sora started a ball at the 15-centimeter mark on a long tape measure. She then rolled it forward 6 centimeters. Before it stopped rolling, the ball would settle back toward her one unit. She continued this pattern until the ball reached the 60-centimeter mark. How many times did Sora roll the ball?
Answer to Brian's Math Magic Trick #2: Come on, you should know that there are no elephants in Denmark! To find out how this stunning act of magic works, go to my website: www.BrianLeaf.com/Elephants.
- C So easy. Just continue the sequence until you have seven terms: 3, 6, 12, 24, 48, 96, 192.
- or 0.666. Still easy! Just continue the sequence until you have six terms: 112, 54, 18, 6, 2,
- 19 Great vocab review! A prime integer is a number that is only divisible by 1 and itself. If the least number in the sequence is 11, the numbers must be 11, 13, 17, 19.
- 9 This "medium" question is easy for us. Remember to underline the vocab; we are looking for the first odd number in the sequence. 12, 8, 10, 9.
- D Just follow the directions closely to get the sequence: 1, 8, 22, 50, 106, 218. Then, to find the average, just add the numbers and divide by how many there are: 405/6 = 67.5.
- B Draw a diagram to get the feel for this question. SAT Crasher's Rule #22: If a picture is described, draw it. The diagram allows you to see that on each roll the ball advances 6 – 1 = 5 cm. Since she is rolling it from the 15–cm mark to the 60-cm mark, the ball will travel 45 cm. So 45 cm divided by 5 cm per roll will need 9 rolls since 45/5 = 9.
Go to: Tip #40
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