Subtraction I

la Billy Thompson likes to play ball just as you and I do but that ball it isn't much good anymore is it Billy would like to buy a new ball but there are some other things he needs to buy first and he's not sure he has enough money Billy has counted his money there's two $23 he needs some paints that will cost 65 and he wants a bat that cost $129 added together they would cost $1.94 that's the same as 194 pennies for the paint and the back and he has 223 pennies can Billy Buy the ball too how much will it cost Billy doesn't really have the ball yet but let's pretend it's here where we can see it oh that's a Dandy ball and it will cost 75 75 will Billy have enough left to buy the ball just how much will be left after he buys the paint and the bat he needs 194 pennies and he has 223 pennies so Billy can subtract to find out how much will be left say just a minute Billy that was interesting but just what did you do let's make sure everyone understands how to subtract let's do it with your money on the floor the money is the same as 223 pennies here are 1 2 3 4 5 6 7 8 9 10 pennies but it would take Billy a long long time to count all the pennies and put them in piles of 10 there 10 pennies in each pile and three pennies left over now 10 pennies are the same as one dime so we'll change each pile of pennies to a dime and put them in piles of 10 with two dimes left over but 10 dimes are the same as $1 so let's change each pile of Dimes to $1 $2 and two dimes and three pennies and that's what our number stands for the three stands for the three pennies this two stands for the two dimes and this two stands for the $2 this is the unit's place this is the 10's place and this is the hundred's place now what is the number we want to subtract 194 that's the cost of the paints and the B just what does 194 stand for the four stands for 4 pennies what does the nine stand for what does the one stand for all right now let's subtract four from three we can't take four pennies away from three we need more pennies before we can subtract let's change one of the dimes to a pile of 10 pennies now we have one dime and 13 pennies and with the numbers will do the same change one of the 10 to 10 units there is one 10 left we can subtract four from 13 four from 13 leaves nine now we must subtract the 10 nine 10 from 110 we have only one dime we can't take nine away so we'll need more dimes let's change one of the dollars to a pile of 10 dimes now we have $1 and 11 dim and with the numbers we'll do the same thing change one of the two 200s to 10 10 that leaves 100 now we can subtract 9 10 from 11 t nine dim from 11 dim leaves two dim next we'll subtract the hundreds 100 from 100 leaves nothing how much is left two dimes and 9 pennies 29 2 10 and 9 units 29 now let's see if we can subtract again with just the numbers on the Blackboard four from three leaves we'll have to change one of the 10 to 10 units we have one 10 left now we can subtract four from 13 now 910 from 110 will have to change one of the hundreds to 10 10 leaving 100 now we can subtract 9 10 from 111 then 100 from 100 and that's how much money he will have left but Billy should check to be sure he didn't make a mistake how should Billy check well let's see suppose from these nine pennies we subtract four pennies how many are left five of course now if we add four pennies to the five that are left how many do we have that's right nine pennies so whenever we subtract we can check our answer by adding now we'll add 194 and 29 there Billy checked his subtraction by adding and he found the same number he started with so he must have subtracted right and now we know that Billy will have 29 cents left after he buys the paints and the bat can he buy a new ball too well the ball will cost 75 and Billy will have only 29 cents left that's not enough is it so Billy can't buy the ball until he has saved some more money if we subtract we'll know how much more Billy will have to save nine from five what do change one of the 10 to 10 units 9 from 15 is six we used one of the 10 so we have only six t left 2 10 from 6 T is four how much more money will Billy need to buy the ball now what should Billy do to check and be sure he didn't make a mistake why check by adding 29 and 46 let's all add with Billy now we know that Billy subtracted right Billy subtracted and found out that he can buy the set of paints and the bat and still have 29 cents left and he found that as soon as he has saved 46 cents more he can buy a ball too we found out how to subtract we know that this is the unit's place and this is the 10's place and if we don't have enough units to subtract we can change 110 to 10 units subtraction is easy