Count : To count means to find out the number of objects by adding one for every object.

Number : A number $x$ is a mathematical symbol representing a quantity.

Count down by 5.

The correct answer is 43. Counting down by 5, you get 48, 47, 46, 45, 44, 43.

Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Hundreds digit : The hundreds digit is the third digit left of the decimal point. It counts multiples of hundred.

Ones digit : The first digit left of the decimal point (or the digit furthest to the right if there is no decimal point). It counts multiples of 1.

Tens digit : The tens digit is the second digit left of the decimal point. For example 31.2 and 32 both have tens digits equal to 3.

Separately add the ones digits, the tens digits and the hundreds digits and then combine the results.

The correct answer is 1,447. 557+890=500+800+50+90+7+0=1,300+140+7=1,447

Division : Division is the mathematical operation that divides objects equally into groups. More generally $x\div y$ is defined as the number that if multiplied by $y$ equals $x.$

Favorable outcome : In a random experiment the favorable outcomes are the outcomes of the event of which we want to calculate the probability. For example if we want to calculate the probability of throwing an even number with a dice the favorable outcomes are 2, 4 and 6.

Non-favorable outcome : When trying to calculate the probability of an event, the non-favorable outcomes are the ones that are not part of that event.

Number : A number $x$ is a mathematical symbol representing a quantity.

Outcome : A result of a random experiment.

Possible outcome : Any outcome of a random experiment.

Probability : A probability is a number between 0 and 1 that describes how likely an outcome is. For discrete events that are equally likely the probability can be calculated by dividing the number of favorable outcomes by the number of possible outcomes.

Reduced fraction : A reduced fraction (or simplified fraction or fraction in simplified form or fraction in simplest form) is a fraction $\frac{a}{b}$ such that $a$ and $b$ do not have any common factors bigger than 1. For example the reduced fraction of the fraction $\frac{4}{6}$ is $\frac{2}{3}.$

Divide the number of favorable outcomes by the number of possible outcomes.

The correct answer is 7/8. There are 8 possible outcomes (each of the three coins can land on heads or tails). The one non-favorable outcome is that all three land on tails, the other 7 outcomes are favorable. Dividing the number of favorable outcomes by the number of possible outcomes we get a probability of $\frac{7}{8}.$