You are here:

Advertisement

Hello, and thank you in advance for your time.

I have a question that I am stuck on.

Ladybirds eat greenfly. On one bush there are enough greenfly to feed 9 ladybirds for 4 hours.

(a) How long would the greenfly last if there were only 6 lacybirds?

(b) How many bushes owuld be needed to feed 36 ladybirds for 2 hours?

Re (a) my thinking has been as follows....enough greenfly to feed 9 ladybirds for 4 hours would mean 18 ladybirds for 2 hours. Thus every 9 extra ladybirds equates to 120 minutes less eating time, or for every 3 extra ladybirds, 120/3 = 40 minutes less eating time. And conversely, for every 3 fewer ladybirds, this would mean 40 minutes extra eating time. And thus, for 6 ladybirds, as 6 is 3 fewer than the 9 in the question, that would mean 40 minutes extra eating time, so that would be 4 hours + 40 minutes.

But....I saw someone else on-line suggest that:

One bush allows 9 ladybirds to eat for 4 hours.

That's 36 "eating hours" in total.

If there were only 6 ladybirds, then the 36 hours would last them 6 hours.

And his 6 hours answer is very different to my 4 hours 40 minutes answer! I wonder if you could possible enlighten me, please?

And as for the second question, I am thinking 2 bushes, but am open to correction.

Many thanks indeed

Denise Byrne

The other person is correct. 1 bush = 36 hrs of eating time. 1 ladybird eats 1/36 of the greenfly in one hr, therefore if there are 6 eating, they eat 6/36 of the greenfly in 1 hr so the green fly will last 6 hrs. You are correct on the second part. If one ladybird eats 1/36 of a tree in 1 hr, 36 ladybirds would eat one tree in one hr, so to feed them for 2 hrs, they'd need 2 trees.

I can answer questions in basic algebra and any grade school math.

Love math, currently helping my nephew get through Intermediate Algebra.**Education/Credentials**

I majored in Math Ed in college (but decided not to teach), so have over 40 credits of math.