What is the third missing term in the series?
15) 1.3, 2.6, 5.2, 10.4,

20.8

The reason is because:

1.3+1.3=2.6

2.6+2.6=5.2

5.2+5.2=10.4

And... 10.4+10.4=20.8

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step-by-step explanation:

1. practice, practice & more practice

2. review errors

3. master the key concepts

do not try to memorise the processes.

4. understand your doubts.

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7. apply maths to real world problems.