Which equals 29^2 x .01
=> ((28 x 30) +1) X .01
=> (840 + 1) x .01
=> 8.41
28 x 30 is an easy mental calculation, as is adding 1, as is moving the decimal place over 2 places. I am teaching this to 4th graders, in two weeks. % to decimal is next week. They can square 2-digit numbers in their heads, already.
33% of 7 = 7% of 33
Bitch, this only works for certain easy maths.
29% of 29 is 29% of 29
Fuck, this trick sucks.
Which equals 29^2 x .01 => ((28 x 30) +1) X .01
=> (840 + 1) x .01 => 8.41
28 x 30 is an easy mental calculation, as is adding 1, as is moving the decimal place over 2 places. I am teaching this to 4th graders, in two weeks. % to decimal is next week. They can square 2-digit numbers in their heads, already.
((30 x 30)-30-29) x .01, easy
33% is the easy one… 1/3 of 6 is 2, 1/3 of 1 is 0.33… 2.33…
1% of 33 is .33
.33 × 7 =
.3 x 7 = 2.1
.03 x 7 = .21
21 + 2.1 = 2.31
So
7% of 33 = 2.31
You could also do
33% of 7
10% of 7 is .7
1% of 7 is .07
So 11% is .77
.77 × 3 =
.7 × 3 = 2.1
.07 × 3 = .21
2.1 + .21 = 2.31
That’s pretty damned intensive for a trick that’s supposed to make the maths easier.
Who said math will be ever easy?