diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 56fe02359..72f4048d5 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -1,30 +1,44 @@
 package pl.edu.agh.mwo.invoice;
 
 import java.math.BigDecimal;
-import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
 
 import pl.edu.agh.mwo.invoice.product.Product;
 
 public class Invoice {
-    private Collection<Product> products;
+    private Map<Product, Integer> products = new HashMap<Product, Integer>();
 
     public void addProduct(Product product) {
-        // TODO: implement
+        addProduct(product, 1);
     }
 
     public void addProduct(Product product, Integer quantity) {
-        // TODO: implement
+        if (product == null || quantity <= 0) {
+            throw new IllegalArgumentException();
+        }
+        products.put(product, quantity);
     }
 
-    public BigDecimal getSubtotal() {
-        return null;
+    public BigDecimal getNetTotal() {
+        BigDecimal totalNet = BigDecimal.ZERO;
+        for (Product product : products.keySet()) {
+            BigDecimal quantity = new BigDecimal(products.get(product));
+            totalNet = totalNet.add(product.getPrice().multiply(quantity));
+        }
+        return totalNet;
     }
 
-    public BigDecimal getTax() {
-        return null;
+    public BigDecimal getTaxTotal() {
+        return getGrossTotal().subtract(getNetTotal());
     }
 
-    public BigDecimal getTotal() {
-        return null;
+    public BigDecimal getGrossTotal() {
+        BigDecimal totalGross = BigDecimal.ZERO;
+        for (Product product : products.keySet()) {
+            BigDecimal quantity = new BigDecimal(products.get(product));
+            totalGross = totalGross.add(product.getPriceWithTax().multiply(quantity));
+        }
+        return totalGross;
     }
 }
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index 318de9ac9..cd0f86a48 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -10,24 +10,28 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
+        if (name == null || name.equals("") || price == null || tax == null || tax.compareTo(new BigDecimal(0)) < 0
+                || price.compareTo(new BigDecimal(0)) < 0) {
+            throw new IllegalArgumentException();
+        }
         this.name = name;
         this.price = price;
         this.taxPercent = tax;
     }
 
     public String getName() {
-        return null;
+        return name;
     }
 
     public BigDecimal getPrice() {
-        return null;
+        return price;
     }
 
     public BigDecimal getTaxPercent() {
-        return null;
+        return taxPercent;
     }
 
     public BigDecimal getPriceWithTax() {
-        return null;
+        return price.multiply(taxPercent).add(price);
     }
 }
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
index 8dce08e28..920b9a99c 100644
--- a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -23,24 +23,24 @@ public void createEmptyInvoiceForTheTest() {
 
     @Test
     public void testEmptyInvoiceHasEmptySubtotal() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
     public void testEmptyInvoiceHasEmptyTaxAmount() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTax()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTaxTotal()));
     }
 
     @Test
     public void testEmptyInvoiceHasEmptyTotal() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
     public void testInvoiceHasTheSameSubtotalAndTotalIfTaxIsZero() {
         Product taxFreeProduct = new TaxFreeProduct("Warzywa", new BigDecimal("199.99"));
         invoice.addProduct(taxFreeProduct);
-        Assert.assertThat(invoice.getTotal(), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(invoice.getNetTotal(), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
@@ -48,7 +48,7 @@ public void testInvoiceHasProperSubtotalForManyProducts() {
         invoice.addProduct(new TaxFreeProduct("Owoce", new BigDecimal("200")));
         invoice.addProduct(new DairyProduct("Maslanka", new BigDecimal("100")));
         invoice.addProduct(new OtherProduct("Wino", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("310"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("310"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
@@ -59,7 +59,7 @@ public void testInvoiceHasProperTaxValueForManyProduct() {
         invoice.addProduct(new DairyProduct("Kefir", new BigDecimal("100")));
         // tax: 2.30
         invoice.addProduct(new OtherProduct("Piwko", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("10.30"), Matchers.comparesEqualTo(invoice.getTax()));
+        Assert.assertThat(new BigDecimal("10.30"), Matchers.comparesEqualTo(invoice.getTaxTotal()));
     }
 
     @Test
@@ -70,7 +70,7 @@ public void testInvoiceHasProperTotalValueForManyProduct() {
         invoice.addProduct(new DairyProduct("Maslo", new BigDecimal("100")));
         // price with tax: 12.30
         invoice.addProduct(new OtherProduct("Chipsy", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("320.30"), Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(new BigDecimal("320.30"), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
@@ -81,7 +81,7 @@ public void testInvoiceHasPropoerSubtotalWithQuantityMoreThanOne() {
         invoice.addProduct(new DairyProduct("Kozi Serek", new BigDecimal("10")), 3);
         // 1000x pinezka - price: 10
         invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
-        Assert.assertThat(new BigDecimal("50"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("50"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
@@ -92,7 +92,7 @@ public void testInvoiceHasPropoerTotalWithQuantityMoreThanOne() {
         invoice.addProduct(new DairyProduct("Chedar", new BigDecimal("10")), 3);
         // 1000x pinezka - price with tax: 12.30
         invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
-        Assert.assertThat(new BigDecimal("54.70"), Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(new BigDecimal("54.70"), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test(expected = IllegalArgumentException.class)