Engineers are working on a feature on a cell phone. The new feature would cost a cell phone user $0.25 for each use. If the user tried the feature 15 times, what would the extra cost for the use of the feature be on the cell phone bill?

And that 5 is half of 10

Find out what ten times the value is then add half of that and you have your answer. '~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

15 uses is ten uses plus 5 uses

The extra cost is $3.75

In a word problem like this, the maths is not difficult, but we need to find all the information first.

The facts we need are as follows about the new feature.

Users have to pay to use it. EACH time it is used costs $0.25 The user tried it 15 times. He will have to pay more on his bill.

Multiplication is the short cut for repeated adding.

A neat way to multiply with 25's is to use the fact that 4x25 =100. Every time there are four 25's we count 100.

A much quicker way is to divide 15 by 4 to find how many groups of 100 we have. Each remainder is another 25.

The extra cost for using the feature on the cell phone bill would be $3.75. This is calculated by multiplying the cost per use ($0.25) by the number of times the feature is used (15):

[ \text{Extra cost} = \text{Cost per use} \times \text{Number of uses} ] [ = 0.25 \times 15 \] \[ = 3.75 ]