Transcript Problems like 23 + ? = 71

Problems like 23 + …….. = 71
I am learning to solve problems like 13 + ……. = 91 by
jumping up by a tidy number on a number line, then jumping
back a small number
Numbers like
10, 20, 30, 40
etc.
Means add (+)
Means
subtract
(-)
SAMPLE PROBLEM
Sam lives at the green house which is number 34 on the
number line. How many numbers does he have to pass to get
to number 82 where his friend lives?
34 + ? = 82
SAMPLE PROBLEM
34 + ? = 82
Step 1: Draw a number line with your starting
point and end point.
34
82
SAMPLE PROBLEM
34 + ? = 82
Step 2: Choose a tidy number to jump up
which takes you just past your target. Then
write it on your number line.
60 Takes me way to far. I will
Adding 40 only gets me to
have to try again
74. That’s not far enough!
50 takes me just past 82 so this is
the best number to jump.
34
82
SAMPLE PROBLEM
34 + ? = 82
Step 3: Jumping up 50 took me a little too
far. I now have to jump back 2 so I can get
to number 82
34
82
SAMPLE PROBLEM
34 + ? = 82
Step 4: You jumped up 50 and back 2 (50 – 2).
So you jumped up 48 numbers. Than means…
34 + 48 = 82
34
82
Now let’s try one together
Fred the frog lives on lily pad 15. He wants to visit his friend
on lily pad number 61. How far does he need to jump?
15 + ? = 61
Now let’s try one together
15 + ? = 61
Step 1: Draw a number line with your starting
point and end point. Do this now on a piece of
paper.
Now let’s try one together
15 + ? = 61
Step 2: Choose a tidy number to jump up which
takes you just past your target number (61).
Do this now.
Now let’s try one together
15 + ? = 61
Step 3: Now find the number you must jump
back to get to your target number.
Add this to your drawing now.
Now let’s try one together
15 + ? = 61
Step 4: Now work out how far you had to jump.
(subtract your little jumps back from your big
jump up.)
Do this now.
So…
15 + 46 = 61
Now try these questions on your own.
1) 17 + ? = 24
6) 18 + ? = 59
2) 23 + ? = 62
7) 12 + ? = 71
3) 56 + ? = 82
8) 56 + ? = 82
4) 34 + ? = 63
9) 34 + ? = 41
5) 15 + ? = 91
10) 15 + ? = 42
Only click again if you have completed all the questions
on the previous slide and you are ready to see the
answers.
1) 7
6) 41
2) 39
7) 59
3) 26
8) 26
4) 29
9) 7
5) 76
10) 27
Need some more practise? Try Pg46 of Teacher Tools Addition and
Subtraction Book Numeracy resources