### Improve math skills of your kids - Learn step-by-step arithmetic from Math games

Math: Unknown - Step-by-step math calculation game for iOS.

Math: Unknown is much more than a math game. It is a step-by-step math calculation game which will teach users how to calculate in the correct order rather than just asking only the final calculated results.

The app consists of four basic arithmetic operations which are addition, subtraction, multiplication and division. In order to get started, users who are new to arithmetic can learn from animated calculation guides showing step-by-step procedures of solving each type of operation. It is also helpful for experienced users as a quick reference.

Generally, addition and subtraction may be difficult for users who just start learning math especially when questions require carrying or borrowing (also called regrouping). The app helps users to visualize the process of carrying and borrowing in the way it will be done on paper. Once users understand how these operations work, they are ready to learn multiplication and division.

For most students, division is considered as the most difficult arithmetic operation to solve. It is a common area of struggle since it requires prior knowledge of both multiplication and subtraction. To help users understand division, the app uses long division to teach all calculation procedures. Relevant multiplication table will be shown beside the question. Users will have to pick a number from the table which go into the dividend. Multiplication of selected number and divisor is automatically calculated, but the users have to do subtraction and drop down the next digit themselves. Learning whole calculation processes will make them master it in no time.

Math: Unknown is a helpful app for students who seriously want to improve arithmetic calculation skills.

### Timing Belts

Timing belts solve the slip problems of flat, O ring, and V belts by using
a flexible tooth, molded to a belt that has tension members built in. The
teeth are flexible allowing the load to be spread out over all the teeth in
contact with the pulley. Timing belts are part of a larger category of
power transmission devices called synchronous drives. These belt or
cable-based drives have the distinct advantage of not slipping, hence the
name synchronous. Synchronous or positive drive also means these belts
can even be used in wet conditions, provided the pulleys are stainless
steel or plastic to resist corrosion.

Timing belts come in several types, depending on their tooth profile
and manufacturing method. The most common timing belt has a trapezoidal
shaped tooth. This shape has been the standard for many years,
but it does have drawbacks. As each tooth comes in contact with the mating
teeth on a pulley, the tooth tends to be deflected by the cantilever
force, deforming the belt’s teeth so that only the base of the tooth
remains in contact. This bending and deformation wastes energy and
also can make the teeth ride up pulley’s teeth and skip teeth. The deformation
also increases wear of the tooth material and causes the timing
belt drive to be somewhat noisy.

Trapezoidal Tooth Timing Belt

Several other shapes have been developed to improve on this design,
the best of which is the curved tooth profile. A trade name for this shape
is HTD for High Torque Design. Timing belts can be used at very low
rpm, high torque, and at power levels up to 250 horsepower. They are an
excellent method of power transfer, but for a slightly higher price than
chain or plastic-and-cable chain

HTD Timing Belt Tooth Profile