200 mangoes at 4 for N2.50
$⟹$ Total cost price = $\frac{200}{4}\times N2.50$
= N 125.00
Since 30 mangoes got spoilt $⟹$ Left over = 200 - 30
= 170 mangoes
170 mangoes at 2 for N 2.40
$⟹$ Total selling point = $\frac{170}{2}\times N2.40$
= N 204.00
Profit : N (204.00 - 125.00) = N 79.00
% profit = $\frac{79}{125}\times 100$
= 63.2% profit.