Line the numbers up, one above the other.  Add 4 and 5 to get 9.  Add 2 and 3 to get 5.  The answer is 59.

First, identify which number is in the hundreds place.  The hundreds place is 3 places to the left of the decimal.  In this case, 3 is in the hundreds place.

If the numbers to the right of the 3 are 50 or more, then we will round it up to 4.  If they are less than 50, we will leave the 3 the same.  Here, we have 42, so the 3 will remain the same.  The two numbers to the right become zeroes.

We round 342 down to 300.  The 2 in the thousands place remains the same.

To find out what number to subtract 0.7 from to get 2.8, just do the opposite - add 0.7 to 2.8.

$\displaystyle 0.7+ 2.8 = 3.5$

The least number is 1, followed by 3, then 6 and finally, 7.

$\displaystyle \fn_cm \fn_cm Line\;up\;the\;numbers\;and\;add\;straight\;down.$

    $\displaystyle 100$

$\displaystyle \underline{+350}$

    $\displaystyle 450$

$\displaystyle x-35=135$

    $\displaystyle \underline{+35\;\;\;+35}$ 

  $\displaystyle x=135+35$

   $\displaystyle \fn_cm 1\not{3}^{4}\: 5$

  $\displaystyle \fn_cm \fn_cm \fn_cm \underline{+\;\;3\;5}$

     $\displaystyle 1\: 7\: 0$

$\displaystyle 5+5=10\rightarrow \;Carry\;the\;1.\;Add\;the\;1\;to\;the\;3\;in\;1\underline{3}5.$

$\displaystyle 4+3=7$

$\displaystyle 1+0=1$

$\displaystyle \fn_cm \fn_cm \fn_cm \fn_cm Line\;up\;the\;numbers\;and\;add\;straight\;down.$

$\displaystyle 5+\, 9=14$

$\displaystyle \fn_cm Carry\;the\;1\;from\;the\;\underline{1}4.\;Add\;the\;1\;to\;the\;0\;in\;205.$

$\displaystyle 1+0=1$

$\displaystyle 2+0=2$

    $\displaystyle \fn_cm 2\not{0}^{1}\: 5$

 $\displaystyle \fn_cm \fn_cm \fn_cm \fn_cm \fn_cm \fn_cm \fn_cm \underline{+\;\;\;\;\;\;\: 9}$   

     $\displaystyle \fn_cm \fn_cm 2\;\;1\: 4$    

Line up the numbers vertically. Add the ones place first $\displaystyle (5+9=14)$. Keep the 4, carry the 1. Then add the 3 digits in the tens place $\displaystyle (1+3+4 = 8)$. Keep the 8. Then add the hundreds place $\displaystyle (7+5=12)$. The sum is 1284

One quarter is $\displaystyle 25\cent$, one dime is $\displaystyle 10\cent$, and one nickel is$\displaystyle 5\cent$.

Three quarters is $\displaystyle 75\cent$, 2 dimes is $\displaystyle 20\cent$, and one nickel is $\displaystyle 5\cent$. If you add these three values you get $\displaystyle \$1$.

To find the sum, you need to add. Line up all numbers vertically. Since one number has a decimal to the tenths place, one has a decimal to the hundredths place, and one has no decimal, be extra careful to line up the digits correctly! To help you, add a zero to the end of 2.4, and add two zeroes to the end of 55 so that all the digits line up correctly.

$\displaystyle \begin{matrix} &\ 2.40 \\ & 55.00\\ + & \ 6.21 \end{matrix}$

Now, add down each column, starting on the right side and moving to the left.

$\displaystyle 2.40 + 55.00+ 6.21 = 63.61$

The sum is 63.61.