@howiehua.bsky.social This question made me think of a 4th grader I tutor who always has unusual ways to do mental math. I shared your video with her tonight. Her method:
10% of 250 is 25
1% is 2.5
3% is 7.5
7% is 10% - 3% so the answer is 25 - 7.5 = 17.5.
Comments
It's so interesting how we all have different ways of figuring it out.
= 7 x 250/100
= 7 x 2.5
= 7 x 5/2
= 35 /2
= 17.5
I have two 100%'s and one 50%. 7 + 7 + 3.5 = 17.5
100% of 7 = 7
200% = 14
50% = 3.5
--> 250% of 7 = 17.5
*why this "switcheroo" works:
A% of B = B% of A
(A/100) • B = (B/100) • A
both = (AB)/100
#MathStratChat #iTeachMath
7/4*10
70/4
17.5
10% of 250 is 25
1% is 2.5
3% is 7.5
7% is 10% - 3% so the answer is 25 - 7.5 = 17.5.
She always uses place value effectively!
7x25 is almost 8x25 which is 200.
25 less is 175.
175 is too big to be 7% of 250, and 1.75 is too small, so the answer must be 17.5
1% of 250 is 250÷100=2.5.
2% of 250 is twice that, so 5.
4% of 250 is twice that, so 10.
7% of 250 is the total, so 17.5.
10% of 250 is 250/10 = 25
1% of 250 is 10% of 25 = 2.5
25 - 3*2.5 = 17.5
I like your double doubles more though! 😜
2.5 × 7 is 14 + 3.5 = 17.5
14 + 3.5 = 17.5