Doubling 2-digit numbers can be quite easy or fairly tricky; it all depends on the numbers. For a number such as 23, doubling is easy as the tens and units can be doubled in your head in either order and can be easily remembered.
However, doubling 37 leads to more complex mathematical thinking as at least three separate operations are needed to reach the correct answer. Probably the easiest way is to double the 30 to make 60. Holding 60 in the back of your mind add the 7 to make 67 and then add the 7 again to make 74. Another way is to double the 30 to make 60 and then double the 7 to make 14 and then add the 60 and the 14 to make 74.
There are other ways, including doubling 40 to make 80 and taking 6 away (double 3) to reach 74. It is always a good idea to see how children tackle these types of questions, ask them what they did and see if it is an efficient way.
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