Update README.md

###### 23. What's the output?

The Answer description was not clear as the reason is that the variable declared with let couldn't be redeclared.

Author: Mohammed-Nasif

README.md

@@ -739,7 +739,7 @@ console.log(num);
 
 With the `var` keyword, you can declare multiple variables with the same name. The variable will then hold the latest value.
 
-You cannot do this with `let` or `const` since they're block-scoped.
+You cannot do this with `let` or `const` since they couldn't be redeclared.
 
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