Estimate 2,145 plus 123 by rounding
each number to the tens place.
In this question, we have to
estimate the sum of our two numbers by rounding each number to the nearest ten. Let’s start by rounding 2,145 to
the nearest ten. The tens digit in 2,145 is a four,
worth 40. So we know 2,145 comes between
2,140 and 2,150. So to help us decide whether to
round our number down to 2,140 or up to 2,150, we need to look to the ones
digit. The ones digit is a five. If the ones digit is worth five or
more, we have to round up to 2,150. So the nearest 10 to 2,145 is
2,150. We had to round up.
Let’s round our next number to the
nearest ten. The tens digit in 123 is a two,
worth two 10s. So we know the two 10s our number
is between are 120 and 130. To help us decide whether to round
down to 120 or up to 130, we need to look at the ones digit. We know that three is less than
five, so we have to round down to 120. Now all we need to do is add
together 2,150 and 120, which is 2,270. We estimated 2,145 plus 123 by
rounding each number to the tens place. Our estimate is 2,270.