Congratulations to the courageous individuals, Nathaniel and Maureen, who provided a solution to the question in my last blog – Nathaniel for his ‘bald’ answer and Maureen for showing working and justifying her solution. My only feedback, as we are aiming for excellence, is that the question involved units ($) so the answer should have included $.
The answer was $99.
10% of 100 is 10 so 100 increased by 10% is 110. Now 10% of 110 is 11 so 110 decreased by 10% is $99.
This question highlights the power of 10%. To find 10% of an amount we simply divide by 10.
For example, 10% of
230 is 230 ÷ 10 = 23 (remove a zero)
346 is 346 ÷ 10 = 34.6 (move the decimal point back one place)
2.40 is 2.40 ÷ 10 = 0.24 (same as above)
Once we know 10% then we can find 20% by doubling 10%.
For example, 20% of 230 is 2 × 23 = 46
Once we know 10% then we can find 5% by halving 10%.
For example, 5% of 346 is 34.6 ÷ 2 = 17.3
Once we know 10% then we can find 15% by adding 10% and 5% or 25% by adding 20% and 5%.
For example 15% of 2.40 is 10% + 5% = 0.24 + 0.12 = 0.36
Being able to calculate 10% is very useful but it comes into its own when shopping during sales times. May the power of 10% be with you!
Now, for this week’s challenge. Place brackets in the following statement to make it true:
2+3 × 5-3 ÷6+1=2
I hope to see even more courageous people having a go at this one.
Dylan says
2+(3×5)-3?(6+1)=2
Nathanael says
(2+3×5-3)/(6+1)=2
/= division sign