Number Sense Blog

Mathnasium #MathTricks: Divisibility (3-digit Rule for 11s)

Nov 3, 2021

One way to test if a three-digit number is divisible by 11 is to follow the 3-digit rule: the sum of the first and last digits equals the middle digit.   To determine if the number 792 is divisible by 11, we find the sum of seven and two. Se...

Mathnasium #MathTricks: Divisibility (Rule for 3s)

Oct 29, 2021

A number is divisible by 3 if the sum of the digits is divisible by 3.   To determine if the number 87 is divisible by 3, we find the sum of its digits. Eight plus seven gives us a final sum of fifteen. Fifteen is divisible by 3. So,   ...

Mathnasium #MathTricks: Percents (Find 1%)

Oct 27, 2021

Recall that 1% means 1 for each 100, 1 out of 100, or one one-hundredth.   We can divide 1 by 100 to convert 1% to a decimal. 1% is equal to 0.01. Notice that dividing by one hundred moves the decimal point two places to the left.   To...

Mathnasium #MathTricks: Percents (Find 10%)

Oct 25, 2021

Recall that 10% means 10 for each 100, 10 out of 100, or ten one-hundredths.   We can divide 1 by 10 to convert 10% to a decimal. 10% is equal to 0.1. Notice that dividing by ten moves the decimal point one place to the left.   To find...

Mathnasium #MathTricks: Special Percents (Basic)

Oct 22, 2021

“Special percents” are easy to compute because they represent easy-to-calculate amounts.   0% means “none of it” 25% means “a quarter of it” 50% means “half of it” 100% means “all of it” 200% means “all of it, twice”   To f...

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