I am doing revision for my upcoming exams, i came upon this question i thought B was the answer but im wrong.
Yes, you are wrong.
Explanation? Gordon’s estimate is 125% of the real size(100%) according to Darren. Therefore, real size = 40cm/125*100 = 32cm.
All you’ve left now is learn how to fish.
32 cm.
If you add a quarter (25%), then to get back to where you started, you take off a fifth (20%).
This may sound strange at first, but think about it with a simpler example.
How do you get from 10 to 20?
You add 100%. (10 plus 100% of 10 = 20)
How do you get back from 20 to 10?
You take off 50%, not 100%.
20 minus 50% of 20 = 10.
I think the proper term for this is “reciprocals” and that is probably what the lesson and test were about.
Often with maths the best way to get your head round a problem is to do it with simpler numbers.
Note that in the question, they chose 40 because 40 is easy divide by either 4 or by 5 in your head.
Here’s a cycling related example: a Sturmey-Archer 3 speed hub has three gears:
The middle gear is a direct drive.
The top gear is direct drive plus 33.3% (That is, plus a third)
The bottom gear is direct drive minus 25% (That is, minus a quarter.
It’s the same train of gears working in reverse. The “opposite” (reciprocal) of “plus a third” is “minus a quarter”.