How did we get that percentage in question 6 i cannot fin it in my own

Hi Sebastian, 

thanks for reaching out! When you talk about question 6, do you mean the course exam, or a quiz question?

Best, 

365 Eli

Instructors! Let me know if I'm on the right track with my explanation of this answer. (And the original poster meant for the quiz question in section 9 [Price Elasticity of Purchase Probability: Results])

Overall Formula:

E = ΔY/Y * P/ΔP

where, 

E is price elasticity
Y is purchase probability (ΔY is ) 

P is price of product

Given: 

1) The price elasticity of purchase probability of a client at 2.56 is 0.7. Althought this is confusing, I think it means that at price = 2.56, the purchase probability = 0.7

(i.e) P = 2.56

       Y = 0.7

2) While their price elasticity: −1.22

(i.e) E = -1.22

3) If we lower the price of the product by 0.02, the new probability of purchase is? 

(i.e) What is Y new when ΔP = -0.02 

[ ΔY = (Y new - Y)

and ΔP = (P new - P).  Since we are lowering price, (P new - P) is -ve ]

Therefore, 

-1.22 = ΔY/0.7 * 2.56/-0.02

ΔY = 0.0067

(i.e) (Y new - Y) = 0.0067   

        Y new = 0.0067 + 0.7 = 0.7067 or 70.67%

[P.S. I realise the answer is slightly low than the correct answer, so I am not sure if my approach is correct or coincidence]