Question

Rule 1: Multiply by 2, then add 1/3 starting from 1. Rule 2: Add 1/2, then multiply by 4 starting from 0. What is the fourth ordered pair using the two sequences

Answer 1

(10 1/3, 42)

Explanation:

a1 = 1

a2 = a1×2 + 1/3 = 2 1/3

a3 = a2×2 + 1/3 = (a1×2 + 1/3)×2 + 1/3 = a1×4 + 2/3 + 1/3 =

= 4 + 3/3 = 5

a4 = a3×2 + 1/3 = ... = 10 1/3

b1 = 0

b2 = (b1 + 1/2)×4 = (0 + 1/2)×4 = 1/2 × 4 = 2

b3 = (b2 + 1/2)×4 = ((b1 + 1/2)×4 +1/2)×4 = 16×b1 + 16/2 + 4/2=

= 16/2 + 4/2 = 8 + 2 = 10

or (to check we made no mistake)

= (2 + 1/2)×4 = 8 + 2 = 10. => all ok, no mistake

b4 = (b3 + 1/2)×4 = ... = (10 + 1/2)×4 = 40 + 2 = 42

so, the fourth ordered pair (= the fourth elements of each sequence) is therefore (10 1/3, 42)