The question is basically, "How many bits in 1000" and then how many adders to add that many bits.
1000 = 2^n implies that n = log(1000)/log(2)... n = 9.9(etc) bits so 10 bits.
I assume each adder is a 4 bits, so we would need 3 of them!
you need a 10bit adress since the most near total addresses are 1024 (2^10). so the 74LS283 is not able to address 1000, because the maximum addresses is of 2^4 = 16 address.
Solution is to put 3 of them and will end up to a 12 bit address!