Question

The first sequence rule is multiply by 3 starting from 5. The second sequence rule is add 9 starting from 18. What is the first number that appears in both sequences?

27
45
72
135

Answer 1

45

Explanation:

first sequence

s1=5(3)^{n-1}

n=1,2,3,...

5,15,45,135,...

second sequence

s2=18+9(n-1)

n=1,2,3,...

18,27,36,45,,...

so first number appearing in both=45

Answer 2

45

Explanation:

If you start from 5 and use a rule that says to multiply by 3, you get a list of numbers like this:

5, 15, 45, 135...

Because 5×3 is 15. And 15×3 is 45. And 45×3 is 135. You times by 3 to find each next number in the list of numbers.

The second list of numbers says to start with 18 and then add 9. So you get:

18, 27, 36, 45, 54...

27 and 72 are NOT the answer because these numbers are not on BOTH lists. 45 and 135 are on both lists. However, they asked for the first number (lowest or least) so 45 is the correct answer.

45 is the first number that appears in both sequences.