randRange(1, 6) randRange(A + 1, 10) B - A randFromArray([ [$._("Spunky Sam"), "spunky-sam.png"], [$._("Mr. Pink"), "mr-pink.png"], [$._("Orange Juice Squid"), "orange-juice-squid.png"], [$._("Purple Pi"), "purple-pi.png"], [$._("Pants"), "mr-pants.png"], [$._("Old Spice Man"), "old-spice-man.png"], ])

How much does UNKNOWN weigh?

KhanUtil.scale.onChange = function(leftCoef, a, rightCoef, b) { $("#sub-left").prop("disabled", a === 0); $("#add-left").prop("disabled", a === 10); $("#sub-right").prop("disabled", b === 0); $("#add-right").prop("disabled", b === 10); var leftOp = ""; var rightOp = ""; var leftOpSign = (a - A > 0) ? "+" : "-"; var rightOpSign = (b - B > 0) ? "+" : "-"; $(".desc-a").text(abs(a - A)); $(".desc-b").text(abs(b - B)); $("#description1").children().hide(); $("#description2").parent().show(); var desc2Text = ""; var desc4Text = ""; if (a - A !== 0 && b - B !== 0) { leftOp = " \\blue{" + leftOpSign + abs(a - A) + "}"; rightOp = " \\green{" + rightOpSign + abs(b - B) + "}" if (a - A < 0 && b - B < 0) { $("#description1 .opt-1").show(); } else if (a - A < 0 && b - B > 0) { $("#description1 .opt-2").show(); } else if (a - A > 0 && b - B < 0) { $("#description1 .opt-3").show(); } else if (a - A > 0 && b - B > 0) { $("#description1 .opt-4").show(); } } else if (a - A !== 0) { leftOp = " \\blue{" + leftOpSign + abs(a - A) + "}"; if (a - A < 0) { $("#description1 .opt-5").show(); } else if (a - A > 0) { $("#description1 .opt-6").show(); } } else if (b - B !== 0) { rightOp = " \\green{" + rightOpSign + abs(b - B) + "}" if (b - B < 0) { $("#description1 .opt-7").show(); } else if (b - B > 0) { $("#description1 .opt-8").show(); } } else { $("#description1 .opt-none").show(); $("#description2").parent().hide(); } desc2Text = "\\qquad x + " + A + leftOp + (a - A === b - B ? " \\quad=\\quad " : " \\quad\\neq\\quad ") + B + rightOp; $("#description3").children().hide(); if (a - A === b - B) { if (a - A !== 0) { if (a === 0) { $("#description3 .opt-done").show(); desc4Text = "\\qquad x \\quad=\\quad " + X; } else { $("#description3 .opt-notdone").show(); desc4Text = "\\qquad x + " + a + " \\quad=\\quad " + b; } $("#description3").show() $("#description4").parent().show(); } else { $("#description3").hide() $("#description4").parent().hide(); } } else { $("#description3 .opt-different").show(); $("#description3").show() $("#description4").parent().hide(); } KhanUtil.processMath($("#description2")[0], desc2Text, true); KhanUtil.processMath($("#description4")[0], desc4Text, true); }; // TODO(emily): make this faster (don't re-init every time) KhanUtil.scale.init({ unknown: X, leftConst: A, rightConst: B, image: Khan.imageBase + "avatars/" + AVATAR });

reset

This is algebra?

Yep! We can represent the problem with an equation if we let the letter `x` represent UNKNOWN's weight:

`\qquad x + A \quad=\quad B`

You subtracted A from the left side and subtracted B from the right side: You subtracted A from the left side and added B to the right side: You added A to the left side and subtracted B from the right side: You added A to the left side and added B to the right side: You subtracted A to the left side: You added A to the left side: You subtracted B from the right side: You added B to the right side: You haven't added or removed anything from either side, so we can't directly tell what UNKNOWN's weight is from the equation.

``

Simplifying, we can see UNKNOWN's weight: Simplifying, we still can't directly see UNKNOWN's weight: Since you did something different to each side of the equation, the left and right side are no longer equal and you can't tell what UNKNOWN's weight is.

``

Balance the scale with UNKNOWN alone on one side and enter the weight:

[ $("input#answer").val(), KhanUtil.scale.leftConst, KhanUtil.scale.rightConst ]
if (guess[0] === "") { return ""; } if (guess[1] !== 0) { return $._("Make sure %(name)s is alone on " + "one side of the scale.", {name: UNKNOWN}); } if (guess[1] + X !== guess[2]) { return $._("Make sure the scale is balanced."); } return +guess[0] === X;
KhanUtil.scale.setLeftWeight(guess[1]); KhanUtil.scale.setRightWeight(guess[2]);
$("input#answer").val(guess[0]);