which best completes the sequence 20 5 30 6 42 7 ?

56 8 72 9 90 10

my guess would be that it goes like this: 20 5 30 6 42 7 56 8 72 9…

56 8 72 9 90 10 110 11 132 12

20 5 30 6 42 7 56 8 72 9…

20, is (5 x 5) – 5
30, is (6 x 6) – 6
42, is (7 x 7) – 7

The next single digit number has to be 8, so:
56, is (8 x 8) – 8

56
20 / 4 =6
5 x 6 = 30
30 / 5 = 6
6 x 7 = 42
42 / 6 = 7
So we have /4, x 6, /5, x7, /6
The next step would be x 8, hence 56. Next would come /7, then x 9. Giving the next two numbers in the sequence as 8 and then 72.

20 5 30 6 42 7 56 8
the single digit number increase by 1
5*6=30
6*7=42
7*8=56, etc.

56 8 72 9 9010 120 12

Notice the pattern.

First, they divided by 4, then multiplied by 6, then divided by 5, then multiplied by 7, then divided by 6…

7….. Next, they would multiply by 8, divide by 7, multiply by 9…

56, 8, 72…

20
divide by 4
5
times 6
30
divide by 5
6
times 7
42
divide by 6
7
times 8
56 — which is next..

Notice how each “divide by” and “times” increase by one each time…