The TAPE DIAGRAM above shows how we can look at all the parts of the question.
In the top row of boxes, we have what Kevin spent on the balloon. The three dimes are shown as divisions in the first box. Each dime is worth 10 pennies or cents, 10c. So the complete dime box is worth 30c. Then we have the three nickels and each division is a nickel worth 5c. The complete nickel box is worth 15c. Then we have the pennies box with each narrow division representing 1c. The whole penny box is worth 4c.
Then we have the long box which is worth 100c ($1). We partly fill the box with the other three boxes and that leaves a box labelled with a question mark. We need to find out what it’s worth. We need to take away the money for the balloon.
We can do this using NUMBER BONDS. First, though, we want to find out how many cents the balloon costs.
Let’s use the ARROW WAY. 30→45→49. The first arrow is adding 15 to 30: that gives us 5 in the ones position and 1+3=4 in the tens. So we have 45 altogether. The second arrow is adding 4 to 45 to make 49. That’s 49c.
Now the NUMBER BONDS. We can split 100c into 50c+50c and then it’s easy to use one of the 50s to take away 49c leaving 1c, which we add to the remaining 50c to make 51c. So Kevin is left with 51c out of the original 100c.