Intro to Percent Change on Jamboard

This post provides details about an artifact that has a manipulative and visual representation of tax rate and discount rate. These contexts are used as an introduction to percent change. The manipulatives are presented on a Google Jamboard.

Overview

The price or original price is presented as dollar bill. The bill is cut into proportional pieces to show the increase or decrease amount, visually, as a part of the original amount. The pieces can be moved around the Jamboard and replaced by other denominations.

Slides

The slides are presented in the slide show below. They are arranged in the following order. the slides show the different positions of the manipulatives, e.g., how the $20 bill is cut into discount and sales price.

  • Slide 1: 5% Tax Rate for $20 price – compute the total to pay
  • Slide 2: 20% off discount for $20 original price – compute the sales price
  • Slide 3: generic tax rate
  • Slide 4: generic discount rate

Access to Jamboard

Here is a link to the Jamboard. You must make a copy to access it.

Sales Price Entry Point

A pseudo- concrete representation of a sales price problem is shown below. This is what I use as an entry point for teaching these problems.

  • The entire shape represents the total price of $80. This is 100%, which in student language is “the whole thing.”

  • The discount rate is 25%. Cut with scissors to lop off the 25% which also lops off $20, which is the actual discount. Explain to the student that this 25% is part of the “whole thing.”

  • What remains is 75% or $60. This is the “new price” which is called the sales price.

IMG_20180526_165232.jpg

Making Discount Meaningful

_20160210_132333

Educators teaching math typically start with the “mathy” stuff first. For example, for finding the sales price teachers may start with showing students the steps to calculate (photo below).

I start with the concept, either with a pictorial representation or actual objects to represent the underlying concept. In the photo above, I show an object (related to the student’s interest – this student is into weight training) on sale. The $50 circled in yellow represent the original price. I explain the concept of being on sale and discount and show that 20% is $10 to take away (marked out). This leaves $40 (in green) which is the sales price. This allows for conceptual understanding before showing him the “mathy” way of doing the problem.

compute discount