If a farm contains 1250 trees, and each tree produces 160 mangoes, the farm produces
[tex] 1250 \times 160 = 200000[/tex]
This means that [tex] k [/tex] farms produce [tex]200000k [/tex] mangoes.
If you want 1 million mangoes, you must solve the equation
[tex] 200000k = 1000000 \implies k = \cfrac{1000000}{200000} = 5 [/tex]
So, you need 5 farms.