Shop sells orange juice in the following ways: 500 ml bottle for £1.15
1.5 l carton for £2.70 each or 2 cartons for £5
3.5 l carton for £5.75

What's the cheapest way of buying exactly 9 litres with no extra?
Find the amount of each type of bottle or carton you need and the total cost of buying 9 litres.

you didn't give me the choices, so i will just give you the graph so you can look at your choices and choose the right one.

, and

for

step-by-step explanation:

we can analyze the pattern at which the terms increase. let us denote , , , so that we can call

note the following:

the pattern: to get the next term value, we just add the next term number (e.g. 1st, 2nd, to the previous term value (term values are the given numbers in the question, 1, 3, 6, 10, 15,

from , to get to , we add

from , to get to , we add

etc.

we need to form a recursive formula, a formula that has the next term as a function of the previous term. so a possible recursive formula can be

, and for

step-by-step explanation:

the answer is 128