Answer:
Fraction of the people chose a tart = 
Step-by-step explanation:
Given - A group of people went to a coffee shop. Each person chose a
drink and a treat. number of people who chose coffee: number of
people who chose tea = 1:4. Of those who chose coffee, number of
people who chose a muffin number of people who chose a tart =
2:7. Of those who chose tea, number of people who chose a muffin
: number of people who chose a tart = 5:1.
To find - What fraction of the people chose a tart?
Proof -
Let the Total number of People went to a coffee shop = 5x
Now,
As given, number of people who chose coffee: number of people who chose tea = 1:4
⇒Total number of people who chooses coffee = 
= x
Total number of people who chooses tea = 
= 4x
Now,
As given,
Of those who choose coffee, number of people who chose a muffin number of people who chose a tart = 2:7
⇒Total number of people who choose muffin after coffee = 
Total number of people who choose tart after coffee = 
Also,
Given that
Of those who chose tea, number of people who chose a muffin : number of people who chose a tart = 5:1
⇒Total number of people who choose muffin after tea = 
Total number of people who choose tart after tea = 
∴ we get
Total number of people who chooses tart = Total number of people who choose tart after coffee + Total number of people who choose tart after tea
⇒Total number of people who chooses tart = + 
= 
= 
= 
⇒Total number of people who chooses tart =
Now,
Fraction of the people chose a tart = 
= 
=
⇒Fraction of the people chose a tart =
