How is 2 ones the same as 20 tenths?

It's because a tenth means that you've divided it by 10. So if it's 20, it means you're multiplying tenths by 20, leaving you with 2 wholes.

For example, you have 2 cakes and you cut each into 10 slices, the slices are each one tenth of the whole cake, and in total there are 20 tenths.

Think of it as currency, for example

2 ones = 2 of $1 = $2 total tenths of dollar = 10 Cents then

20 x 10 Cents = 200 Cents = $2

so they are the same.

As is 200 hundredths, and so on

d) 30 units^2

area of rectangle = l × b

we know,

length = 10 unit

breadth = 3 unit

applying the formula,

= l × b

= 10 × 3

= 30 unit^2

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