# Video: AQA GCSE Mathematics Foundation Tier Pack 1 • Paper 1 • Question 21

Here are the quantities of ingredients needed to make 20 crepes: 3 eggs, 250 g of flour, 500 ml of milk. a) How much milk is needed for 50 crepes? b) Rob has 12 eggs, 1 kg of flour, and 1.5 L of milk. What is the maximum number of crepes he can make with these quantities?

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### Video Transcript

Here are the quantities of ingredients needed to make 20 crepes: three eggs, 250 grams of flour, 500 milliliters of milk. a) How much milk is needed for 50 crepes? And b) Rob has 12 eggs, one kilogram of flour, and one and a half liters of milk. What is the maximum number of crepes he can make with these quantities?

Starting with part a, we want to make 50 crepes. Our given quantities make 20 crepes. We have to consider how many 20s go into 50. Imagine this whole bar is 50. We could break it up into 20 and 30. We can also break it up into 20, 20, and 10. 20 goes into 50 two whole times. And then, there’s 10 out of 20 remaining, two and one-half.

If we multiply 20 by two and a half, we get 50. We need to use two-and-a-half times the milk if we’re going to make 50 crepes. The original quantity requires 500 milliliters of milk. We need two and a half times that. We can break it up into 500 times two and 500 times one-half. 500 times two is 1000. 500 times one-half or 500 divided by two equals 250. We would need 1250 milliliters of milk.

Moving on to part b, “Rob has 12 eggs, one kilogram of flour, one and a half liters of milk. What is the maximum number of crepes he can make with these quantities?”

We need to take the amount Rob has and divide that by the quantity you need per 20 crepes. We can start with the eggs: Rob has 12. And for every 20 crepes, you need three. 12 divided by three equals four. This tells us that Rob has enough eggs to complete the recipe four times.

But you don’t just need eggs to make the recipe. And so, we need to consider the flour. We know that Rob has one kilogram of flour. But our recipe is measured in grams of flour. We know that one kilogram equals 1000 grams. And that means we can divide 1000 grams by 250 grams. 1000 divided by 250 equals four. Rob has enough flour to make the recipe four times. It seems like he’ll be able to make the recipe four times. But we need to check and make sure he has enough milk to do that.

Rob has one and a half liters of milk. Our recipe tells us the amount of milk we need in milliliters. We can convert one and a half liters to milliliters by multiplying by 1000. One and a half liters equals 1500 milliliters Rob has 1500 milliliters. And for every 20 crepes, you need 500 milliliters of milk. 1500 divided by 500 equals three. Rob only has enough milk to make the recipe three times. And this makes the milk the limiting ingredient.

At this point, we need to remember that what we’re looking for is the maximum number of crepes that he can make. We know that he can make the recipe three times. And we know that each time you make the recipe, it makes 20 crepes. So we multiply three times 20 to get 60. Rob has enough ingredients to make the recipes three times and doing that will make 60 crepes.