A). There are 1,500 mangoes in 10 crates because 150(the mangoes in each crate) times 10(the amount of crates) results in 1,500 crates total.
B). If the crates contained 50 less mangoes, there would be 100 mangoes in each crate. There would be 500 mangoes less than before, which would fit into 5 more crates.