If I add together 436 and 60, what
will the tens digit of the sum be?
This is an interesting question
because it starts off by looking like we need to add together 436 and 60. But as we read the rest of the
question, we can see that we’re not being asked for the sum of these two
numbers. We’re being asked what the tens
digit in the sum is going to be. And you might think to yourself,
“Well, I’m gonna have to work out the answer and then just look at what the tens
digit is.” But there’s a quicker way to solve
the problem, and it involves us understanding what it means to add a multiple of 10
to a three-digit number. So, let’s have a go at solving this
problem the quick way.
And it’s not that difficult; it
just involves us understanding the place value of the numbers that we’re adding. So, if we think about the number
we’re starting with, 436 contains four 100s, three 10s, and six ones. And the number that we’re adding to
this contains six 10s and zero ones and, of course, zero 100s as well. Now, the really important bit about
what we’ve just said is this digit here. The number that we’re adding on to
436 contains six 10s. It doesn’t contain any hundreds,
doesn’t contain ones, just six 10s because six tens equals 60.
Now, as we’ve said already, our
starting number 436 has got three 10s. So if we already have three 10s and
we’re adding on six 10s, what will the tens digit of the sum be? Well, we know that three plus six
equals nine. So, three 10s plus six 10s is going
to make nine 10s. Our answer is going to have the
digit nine in the tens place. So, although we don’t have to,
let’s just write down what the sum would be. It’s still going to have four 100s,
and it’s still going to have six ones. Those digits aren’t going to
change. But the three tens that we started
with are now going to become nine 10s. 436 plus 60 equals 496.
We’ve used our knowledge of place
value here to work out what the tens digit is going to be. If we add 60 to a number that has
three 10s — in this question, it was the number 436, but, you know, it could have
been any number at all — we found that the answer will contain nine 10s. So, the tens digit of the sum of
these two numbers is nine.