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In this video we're going to focus on calculating percentages without the use of a calculator we're going to do it mentally and then we'll confirm our answer with the use of a calculator so here's the first question what is 15% of 200 how can we find the answer to this question mentally well first ask yourself what is 10% of 200 to find 10% of a number simply move the decimal one units or less so 10 percent of 200 is 20 now if 10 percent of 200 is 20 what is 5 percent of 200 5 percent is 1/2 of 10 percent so what is 1/2 of 20 half of 20 is 10 so now with this information how can we find out the value of 15 percent of 200 well since 10 percent plus 5 percent adds up to 15 percent 20 plus 10 must represent the value of 15 percent of 200 which is 30 now to confirm the answer using the calculator is we need to do take 200 and multiply it by 15 percent as a decimal to convert a percentage into a decimal simply divide by 100 15 divided by 100 is 0.15 you can also move the decimal point two units left so those are two ways that you can use to convert a percentage into a decimal now let's multiply 200 by point 15 if you have a calculator go ahead and type this in so 200 times 0.15 is indeed equal to 30 so now you know how to do percentages mentally so let's go ahead and work on some more examples now what is 25% of 300 go ahead and take a minute pause the video work on this example and then once you have your answer unpause it to see if you have the right answer so let's start with 10% of 300 how much does that amount to what is 10% of 300 10% of 300 is simply 30 just move the decimal one units left we'll take off a zero so if that's 10% how much is 20% 20% is twice the value of 10% so if we multiply 30 by 2 we're going to get 60 now to get the 25% we need to find the value of five percent 5% is half of 10% so half of 30 is 15 so now we can find the value of 25 percent 25 is the sum of 20 and 5 so therefore to find the value of 25% we need to add 60 + 15 60 + 15 is 75 so now let's confirm this answer with the use of a calculator let's multiply 300 by 0.25 25 percent as a decimal and this will indeed give you 75 what is 40% of 500 go ahead and work on that question so as we've been doing before let's start with 10% so what is the value of 10% of 500 this is going to be 50 if we drop off a zero and now we can find 40 percent forty percent is simply 10% times four so if we multiply 15 by 4 what will that give us so imagine if you have for $50 bills you have basically 200 4 times 0 is 0 and 4 times 5 is 20 so therefore 40% of 500 is 200 and if you multiply 500 by 0.4 this will also give you 200 as well now let's move on to our next example what is 24% of 80 so let's make it a little bit more challenging go ahead and try that so first let's calculate 10% of 80 10% of 80 is 8 and 20% of 80 is basically 8 times 2 that's 16 now we need to get to 24 percent so it's helpful if we find the value of 1% if 10 percent is 8 then 1 percent is 0.8 basically you move the decimal one units the left or divided by 10 so if one percent is point 8 what is the value of 4% well if 8 times 4 is 32 and then 0.8 times 4 must be 3 points in now to get to 24 percent we need to add 20 percent and 4 percent so basically we need to add 16 and 3 points you so 16 point 0 and 3 point 2 2 and 0 is 2 3 and 6 is 9 so it's 19 point soon so if we multiply 80 by point 2 4 this will give us 19 points in so you can always check your answer with the use of a calculator to make sure you're doing it right what is the value of 33 percent of 120 so now that you know how to do the last example you can do this one so go ahead and try it so as always I'm going to start with 10% since that's a nice number to deal with so what is 10 percent of 120 well if we drop off a 0 10 percent is going to be 12 now we need to find 30 percent our goal is to get up to 33 percent the 30 percent is three times the value of 10% 10 times 3 is 30 so if 10% is 12 then 30% must be 12 times 3 which is 36 now our next thing that we need to find is 1% if we could find the value of 1% we can find the value of 3% now if 10% is 12 1% is basically 12 divided by 10 or 1.2 just move the decimal one units or less so 3% is going to be 3 times 1.2 because 3% is 3 times 1 percent now if 12 times 3 is 36 then 1.2 times 3 must be 346 since we're looking for 33% we need to add 30% plus 3% so we need to add 36 point 0 plus 3

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