3 of 10 grid squares making up the whole will be colored.
Step-by-step explanation:
1/10 is one of ten equal parts. 3/10 is three of those ten equal parts. Essentially, the fraction 3/10 means "three out of ten".
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If the whole is divided into more than 10 parts, 3/10 will be 3 out of every 10. So if there are 20 parts, for example (2 tens), the 3/10 will be 6 of those parts (3 of each of the two tens).