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How would you solve this math problem?? My solution was 47 + 30 - 2 = 75

TheoryNumber3 8 May 16

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8 + 7 = 15.
Carry the 1.
3 + 4 = 7.

That was the way I was taught to do the math.

Yes, me too. I have to imagine I'm writing it down on paper vertically and go down in that process, the ones column and then the tens column, carrying the one.


I simply do it like I was taught in school many moons ago. 47
In my head it's 7+8=15 carry the 1, 4+2+1=7 so 75 is the answer. I am not a mathematician by any stretch though lol.


I HATE MATH! This is why l became a drummer. I only have to count to four.

not if you're playing with Dave Brubeck πŸ˜‰

@TheoryNumber3 That won't be a problem as he is dead. 😁

@Sticks48 well I didn't mean him personally πŸ™‚)))

@TheoryNumber3 l know, but you set that up like a T-ball. 😊

@Sticks48 Yeah I'm good like that πŸ˜‰


20+40 and 8+7 then 60+15=75

That's how I did it, too.


I do it quickly by first adding the 10s column, then the ones column



Add the tens and then, add the ones, then, add both.


Take 2 from the 47 and add it to the 28. 30 +45=75. It's not new math. It's allowing people to use what they know to figure things out instead of just following algorithms that we were forced to use.


15 plus 60

Show your work!


First I did it the old school way: 8 + 7 = 5, carry the 10. 10 + 20 + 40 = 70. 70 + 5.

Then I thought, well that's a nice round number, 75, three quarters (three 25s). I looked back at the original addends. Take 3 from 28 to make one quarter; add it to 47 to make two quarters. Same result, three quarters, 75.

It's similar to the thought process when I'm paying cash and trying to get rid of my pennies, nickels, and dimes and get quarters for change. (Our washers and dryers take quarters, so I'm always hoarding quarters.) If the bill is 87 cents, I try to pay with a dollar and (87 - 75 = ) 12 cents in change (dime and two pennies or nickel and seven pennies). Announce to the cashier that I'm giving "a dollar, twelve" and hope that he or she enters $1.12 into the register and lets the register calculate change due (one quarter). Otherwise the cashier may freeze in utter confusion. (Why is he giving me 12 cents when he is already giving me a dollar, and the bill is only 87 cents?? Help!)

Occasionally, I make a mistake in my head and confuse the cashier and myself. Example: the bill is 97 cents. "Here is a dollar, twelve." Uhhh...

You still use cash????

@TheoryNumber3 Generally just for small purchases.


Yep I would do it the same way as you. Or I would go. 28 + 40 = 68 and seven plus eight always takes you to the next five up, so 75.


maybe this will help


I round 28 to 30 to make it easier to add, then I subtract 2: 47 + 30 = 77 - 2 = 75.


Try to make one number whole add it to the other and then add the remainder from the first number (clear as mud) 28 + 40 and then add the 7 = 75.


My brain recognizes the numbers on the calculator. Using a combination of both the numbers involved and the operators also on the touchpad, my brain instructs my finger to punch the ones necessary for the equation. Once completed it recognizes and utilizes the answer displayed on the screen. Hope that helps.

WOW! That's amazing! You should do a Ted Talk πŸ™‚


. . . a very good read :


I have that book in my collection and I never read it. Maybe it's time πŸ™‚

@TheoryNumber3 That ADDS up πŸ™‚

See my YT video (the Author) above.


30+50=80, -2=78, -3=75. That was β€œnew math” when I went to primary school.


28 plus 40 is 68 then add 7.


I mentioned the book in an earlier comment . . . .
Here is the Author :

uh.... where's my calculator? LMAO!! I'm definitely old school.


I've seen this a couple of times, and my approach was a little different each time.

The first time, I did it like this:
20 + 40 = 60
8 + 7 = 15
60 + 15 =75

The second time, I broke it down differently:
(rounded up to the nearest ten, then subtracted the difference)
30 + 50 = 80
2 + 3 = 5
80 - 5 = 75

When I was young, I probably would have done it the old way:
(add up the ones place first, then the tens place)
7 + 8 = 15 (hold the 5 ones, carry the 1 to the tens)
2 + 4 + 1 = 7 tens
7 concatenated 5 = 75
(or, more accurately, 7 * 10 + 5 = 75)

I know a lot of people in their mid-30s and older complain about new math concepts and techniques, but as an adult I started doing math in my head the so-called new way before I knew what students today are learning. Someone I used to work with complained that she can't assist her child with his math homework anymore because the methods for arithmetic have changed, and I understand the concern, but I also recall how most students when I was in school (even in college) hated math, didn't understand the concepts, and avoided anything involving numbers later on in their coursework (and in life). I was quite good at math and was rather lucky that the old methods didn't deter me from pursuing higher math, science, and programming. Teaching kids to be able to think about numbers in the dynamic ways they're learning now, and the way many of us have learned over time to break numbers down to do math in our heads, is good for them. The aren't confused by places, the aren't carrying numbers from one column to another, they aren't trying to figure out abstract concepts; instead, they're playing with the numbers in a more natural way, thinking of them in ways that are naturally mutable, easily broken down and recombined. The underlying principles remain, but how they're applied is much more intuitive.


I made 28 30 and subtracted two from 47 to get 45 then I added 45 and 30 to get 75.

It sounds like there are many paths to the same location. I was the most popular shopping companion at work because I could calculate rapidly in my head the cost of items that were Marked as certain percentage down. I explained repeatedly how I did it but interestingly not one of my friends ever even tried. for example 60% off meant I multiply the rounded cost by four making a 49.99 item cost $20 or if you needed the actual cost 19.96.

I checked groceries in high school and college and I am so old tax had to be figured in my head. Fortunately they had not discovered percentage point taxation in those days. In other words I practiced lots of mathematical calculations without a pencil in my youth and practice makes perfect.


Unfortunately I have to either write it down on paper or imagine writing it down .Increasingly as I age the second option is used less frequently. That does show the power of the written word, but I managed to avoid that in the Bible.
Children really need to learn that showing your working really does get you marks. I used to advise that pupils should always fill every answer space on an exam paper because sometimes even they do not know that what they are writing is NOT rubbish.


28 + 47 = 75 since adding the 8 and the 7 first give one 15, put the 5 into the singles column, pass on the 1, then add that to the 2+4, ( 1+2+4 = 7),giving you the the sum total of 75.

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