Transcript When one number is near 100

When one number is near a hundred
I am learning to solve some addition and subtraction problems by
adjusting one number to the nearest hundred.
e.g. 198 is close to 200
or 301 is close to 300
Todd has $98 and saves $34 more. How much money does he
have?
Step1: First let’s record how much money he has in two separate
piles.
Step 2: To make this question easier we change $98 into $100. We
do this by taking $2 from the $34.
$10
$10
$10
$10
$10
$10
$10
$10
$10
$10
We now have ten $1 coins which
we swap for a $10 note.
1So the
1 question is now $100 plus $32
1
1
1
1
1
1
1
1
1
1
$98 $100
$10
$10
$10
$100 + $32 = $132
1
1
$34
$32
We can also use this method for numbers just over 100.
Andy has $103 and saves $26 more. How much money does he
have?
Step1: First let’s record how much money he has in two separate
piles.
Step 2: To make this question easier we change $103 into $100. We
do this by moving $3 to the $26.
1
$100
1
1
1
1
1
1
1
1
1
1
1
$103 $100
$10
$10
$26 $29
So the question is now
$100 plus $29
$100 + $29 = $129
Below are the same two problems but this time I have shown how I
like to record my working. You might like to do this too until you are
ready to do the whole process in your head.
98 + 34 = ….
103 + 26 = ….
98 + 34 = ….
+2
-2
100 + 32 = 132
…..
One side is getting bigger by two
and one side is getting smaller by
two because I am moving this
amount from one pile to the
other.
103 + 26 = ….
-3
+3
100 + 29 = 129
…
One side is getting smaller by
three and one side is getting
bigger by three because I am
moving this amount from one pile
to the other.
Now try these questions on your own.
Remember to first change the question then answer.
1) 99 + 32 = ?
100 + 31 = 131
2) 298 + 38 = ?
300 + 36 = 336
3) 197 + 74 = ?
200 + 71 = 271
4) 301 + 27 = ?
300 + 28 = 328
5) 203 + 65 = ?
200 + 68 = 268
Click again when you have
completed each question and
the answer will be displayed.
Need some more practise? Try Pg50 of Teacher Tools Addition and
Subtraction Book Numeracy resources