diff --git a/js/game/model/NumberPlayGameLevel.ts b/js/game/model/NumberPlayGameLevel.ts
index 12bac875..25bf94bc 100644
--- a/js/game/model/NumberPlayGameLevel.ts
+++ b/js/game/model/NumberPlayGameLevel.ts
@@ -90,7 +90,7 @@ abstract class NumberPlayGameLevel {
     this.oldChallengeNumberOne = this.challengeNumberProperty.value;
 
     let newChallengeNumber = this.getRandomChallengeNumber();
-    while ( newChallengeNumber === this.oldChallengeNumberOne && newChallengeNumber === this.oldChallengeNumberTwo ) {
+    while ( ( newChallengeNumber === this.oldChallengeNumberOne ) && ( newChallengeNumber === this.oldChallengeNumberTwo ) ) {
       newChallengeNumber = this.getRandomChallengeNumber();
     }
     this.challengeNumberProperty.value = newChallengeNumber;
diff --git a/js/game/model/NumberPlayGameModel.ts b/js/game/model/NumberPlayGameModel.ts
index 4757d864..8ac4fbb8 100644
--- a/js/game/model/NumberPlayGameModel.ts
+++ b/js/game/model/NumberPlayGameModel.ts
@@ -32,7 +32,7 @@ class NumberPlayGameModel {
     this.subitizeLevels = gameBLevelNumbers.map( gameBLevelNumber => new SubitizeGameLevel( gameBLevelNumber ) );
     this.levels = [ ...this.countingLevels, ...this.subitizeLevels ];
 
-    // the selected game level - null means 'no selection' and causes the view to return to the level-selection UI
+    // the selected game level - null means 'no selection' so that the view returns to the level-selection UI
     this.levelProperty = new Property<SubitizeGameLevel | CountingGameLevel | null>( null, {
       validValues: [ null, ...this.levels ]
     } );
diff --git a/js/game/model/Subitizer.ts b/js/game/model/Subitizer.ts
index 4eb699e0..c25040a2 100644
--- a/js/game/model/Subitizer.ts
+++ b/js/game/model/Subitizer.ts
@@ -280,7 +280,7 @@ class Subitizer {
     const challengeNumber = this.challengeNumberProperty.value;
     let points;
 
-    if ( this.randomOrPredetermined && dotRandom.nextDouble() <= PROBABILITY_OF_PREDETERMINED_SHAPE ) {
+    if ( this.randomOrPredetermined && ( dotRandom.nextDouble() <= PROBABILITY_OF_PREDETERMINED_SHAPE ) ) {
       points = Subitizer.getPredeterminedShapePoints( challengeNumber );
     }
     else if ( this.randomOrPredetermined ) {
@@ -339,7 +339,7 @@ class Subitizer {
 
       // add a new point if it doesn't exist yet and does not overlap with the existing points
       const objectsOverlap = Subitizer.objectsOverlap( points, randomX, randomY );
-      if ( !_.find( points, object => object.x === randomX && object.y === randomY ) && !objectsOverlap ) {
+      if ( !_.find( points, object => ( object.x === randomX ) && ( object.y === randomY ) ) && !objectsOverlap ) {
         points.push( new Vector2( randomX, randomY ) );
       }
     }