List manipulation with Riffle, Partition and Flatten?

Questions
1

I want to create the following list:

{{10,10,a,b},{20,20,a,b},{30,30,a,b},{40,40,a,b}}

I used Riffle and Table to produce the following:

Riffle[
 Table[{10 j, 10 j}, {j, 1, 4}], {{a, b}}]
(*  {{10, 10}, {a, b}, {20, 20}, {a, b}, {30, 30}, {a, b}, {40, 40}} *)

(Note that I am missing a {a,b} for the {40,40} term, so if any one has a better idea, I would take it.)

Partition then gives

Partition[
{{10, 10}, {a, b}, {20, 20}, {a, b}, {30, 30}, {a, b}, {40, 
   40}}, 2]
(* {{{10, 10}, {a, b}}, {{20, 20}, {a, b}}, {{30, 30}, {a, b}}} *)

I tried to Flatten it, but Flatten works too strongly, just deletes the inner braces, even when using its second argument.

What operation should be made to change it to

{{10,10,a,b},{20,20,a,b},{30,30,a,b},{40,40,a,b}}

?

2

Hi Ehud,

There are many ways to generate the list. Here are two

{#, #, a, b} & /@ Range[10, 40, 10]
(* {{10, 10, a, b}, {20, 20, a, b}, {30, 30, a, b}, {40, 40, a, b}} *)

Using Table

Table[{x, x, a, b}, {x, 10, 40, 10}]
(* {{10, 10, a, b}, {20, 20, a, b}, {30, 30, a, b}, {40, 40, a, b}} *)
3

I went round and round in circles, forgetting the easiest way of Table.

Thanks!