title: How do you multiply values in one map with the values in another?
body: <p>If you have two maps (one is mutable, the other is immutable), how would you multiply the values of one with the corresponding values of the other?</p>
  
  <p>For example:</p>
  
  <pre><code>val testA = scala.collection.mutable.Map("£2" -&gt; 3, "£1" -&gt; 0, 
                    "50p" -&gt; 4, "20p" -&gt; 0, "10p" -&gt; 0, "5p" -&gt; 0)
  val testB = scala.collection.immutable.Map("£2" -&gt; 2, "£1" -&gt; 1, 
                    "50p" -&gt; 0.5, "20p" -&gt; 0.2, "10p" -&gt; 0.1, "5p" -&gt; 0.05)
  </code></pre>
  
  <p>Expecting a result of:</p>
  
  <pre><code>val total = scala.collection.immutable.Map("£2" -&gt; 6, "£1" -&gt; 0, 
                    "50p" -&gt; 2, "20p" -&gt; 0, "10p" -&gt; 0, "5p" -&gt; 0)`
  </code></pre>