### Video instructions and help with filling out and completing Fill Form 8815 Subtract

Instructions and Help about Fill Form 8815 Subtract

Hi there and welcome to another video from Hegarty maths it's mr. Haggerty here and in this video we're talking about adding and subtracting with standard form now to start with I want to actually ask you a question I've previously asked you about imagine someone asks you to evaluate 10 squared add 10 to the power of 5 can you imagine what students might do that's a mistake there well what students like to do they like to try and find a quick way of doing things so they might say mmmm 10 are 10 20 I know something about you add the powers so they might say 20 to the power of 7 now that adding the powers with indices only is true when you multiply indices isn't it and remember when I was going through those videos saying to you whatever you do don't feel obliged to do a trick or try and do something you're not sure of the only rule I ever taught you with multiplying indices was the following if you multiply them you keep the base number the same and you can add the powers I also told you if you are dividing them you keep the base number the same let's say and you can subtract the powers but I didn't say anything about if you're adding them or subtracting them I'm afraid if you're adding or subtracting them you've just got to work them out longhand ok so that wouldn't be allowed what you would do just convert that into an ordinary number what does this mean well it means 10 squared 100 and what does this mean 10 to the power of 5 is a hundred thousand so all I want you to do is add a hundred and a hundred thousand that's dead easy that's a hundred thousand 100 isn't it simple as that and if you really really wanted to give it in standard form if you were desperate to write that number in standard form although you know who's to say you need to what would you do well you have to write everything from the first non-zero up to the last non-zero so you'd have to write one point zero zero one and times ten to the power of how much how many digits you've got after the first one one two three four five okay and that would be it but again that answer would be just as good okay okay let's try some questions pause the video and try in the new self if you feel that you can to multiply by 10 to the power of 4 add 3 multiplied by 10 to the power of 3 so I would just convert these to ordinary numbers first that's a 2 with 4 zeros after it 1 2 3 4 ie 20,000 and this here is just going to be add 3,000 isn't it 3 multiplied by 10 to the 3 is going to be 3 with 3 zeros after it now 20,000 add 3,000 that's pretty easy that's 23,000 isn't it there you go no one's asked us to leave it in standard form at the end that's the answer absolutely fine next one same thing this here 10 to the power of 5 is a hundred thousand isn't it so 4 x that must be 400 thousand and what we add in we're adding well 10 to the power of 5 is we said 100,000 so 2 lots of that is 200,000 and 400,000 at 200,000 is simply 600,000 and we're done the next one well 2 multiplied by 10 squared 10 squared 100 so 2 lots of that must be 200 and 1.3 times 10 to the power of 3 that's a thousand 1.3 times 1,000 must be 1,300 and if we add those together we're going to get ourselves 1,500 okay and we're done let's try some more questions here we go now here's the same thing we're adding numbers in standard form but it does say we've got to at the end give our answer in standard form four multiplied by 10 squared is going to be 4 with two zeros after it 400 plus 3 multiplied by 10 to the power 1 is 3 with 1 0 after it this therefore is 430 if I have to write it in standard form I would write for point 3 and remember I'm counting how many digits after my 4 to the 1/2 to the times 10 to the power of 2 and I'm done and the next one we're adding two small numbers here because they're both negative powers of 10 so we're going to write out what this one is as ordinary number it's going to be 4 with three zeroes in front of it 1 2 3 my decimal point goes there and we're adding this here and I'm going to write a 6 with 4 zeros in front of it 1 2 3 4 and my decimal point will go there now if I am adding these up it will be best if I add them up in the column method so I'm going to go over here and just do a quick column method 0.004 and what we're doing is we're adding zero point zero zero zero six and clearly you can see we're going to get zero point zero zero four six aren't we okay there's a real zero there so we know the answer is zero point zero zero four six but we have to write it in standard form so we say four point six times ten to there well there are three zeros before the four so it's going to be to the negative three and we're done why don't you try these ones subtractions so this here 2 x 10 cubed is going to be 2 with 3 zeros after it mm we're taking away 3 x 10 squared.