Answer:
Mary needs $0.18 more
Explanation:
12 mangoes = $13.20
For every 5 mangoes that he bought he got one mango free
This means he bought 10 mangoes (5 mangoes + 1 free mango the first time and 5 mangoes + 1 free mango the second time)
If James paid $13.20 for 10 mangoes, then
Each mango cost = $13.20 / 10
= $1.32
Each mango cost $1.32
Mary wants to by 4 mangoes from the same shop.
Total cost of 4 mangoes = $1.32 × 4
= $5.28
She only has $5.10.
How much more money does she need
Amount needed more = Total amount required - total amount available
= $5.28 - $5.10
= $0.18
Mary needs $0.18 more