задание творческий подход


#1

Не могу понять почему первое условие не выполняется?

var buy = 4000;
var discountedBuy;

if (buy >= 1000 || buy < 3000) {
discountedBuy = buy - (buy / 100 * 5);
}

if (buy >= 3000 || buy < 5000) {
discountedBuy = buy - (buy / 100 * 10);
}

if (buy >= 5000) {
discountedBuy = buy - (buy / 100 * 15);
}

if (buy < 1000) {
discountedBuy = buy;
}