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Ffocws dysgu

Dysga gyfrifo gan ddefnyddio dulliau meddwl ac ysgrifenedig i dynnu rhifau 3 digid drwy ddefnyddio dull meddwl neu ysgrifenedig priodol.

Mae'r wers hon yn cynnwys:

• un fideo
• dau weithgaredd

Learning focus

Learn to calculate using mental and written methods to subtract 3-digit numbers using an appropriate mental or written method.

This lesson includes:

• one video
• two activities

Fideo / Video

Eglurhad o sut i dynnu gan ddefnyddio colofnau.

An explanation of how to subtract using columns.

Nodiadau i rieni

• Rhaid gwahanu’r digidau i mewn i golofnau gwerth lle. Hynny yw, yn y rhif 92, mae 2 o unedau a 9 o ddegau. Wrth wahanu 27 i golofnau gwerth lle, mae 7 o unedau a 2 o ddegau.
• Rhaid gosod y rhif gwreiddiol (y rhif mwyaf) ar y top.
• Yna, rhaid tynnu pob colofn gan ddechrau gyda’r unedau.
• Wrth dynnu’r golofn gyntaf, os oes rhif ar y top sy’n llai na’r rhif ar y gwaelod, rhaid benthyg o’r golofn degau (y golofn i’r chwith). Hynny yw, mae 2 yn llai na 7 felly rhaid cymryd deg o’r golofn degau sy’n newid y 90 i lawr i 80. Yna byddwn yn rhoi’r deg i’r golofn unedau i wneud 12.
• Nawr, gallwn dynnu 7 i ffwrdd o 12 i wneud 5. Rhaid gosod yr ateb 5 yn y blwch ateb o dan yr unedau.
• Nawr, symuda ymlaen i’r golofn degau. Gallet dynnu 2 oddi wrth yr 8 i wneud 6. Rhaid gosod yr ateb 6 yn y blwch ateb o dan y degau.

Notes for parents

• We must separate the digits into place value columns. Therefore, with the number 92, we have 2 units or ones, and 9 tens. When we separate 27, we have 7 units or ones and 2 tens.
• You must place the original number (biggest number) on the top.
• Then, you should subtract each column, starting with the units.
• When subtracting the first column, if the number on top is smaller than the number on the bottom, we must borrow from the tens column (column to the left). In this instance, 2 is less than 7 so we must take ten from the tens column which changes the 90 down to 80.
• Now we can subtract 7 from 12 to make 5. Place the 5 in the answer box under the units.
• Now, move on to the tens column. You can subtract 2 from 8 to make 6. Place the 6 in the answer box under the tens.

Os yw’r rhifau’n rhy uchel neu’n rhy anodd i’w tynnu yn dy ben, ysgrifenna nhw mewn colofnau. Gwahana’r rhifau’n unedau, degau, cannoedd a miloedd. Rhestra’r rhifau mewn colofn a dechreua gyda’r unedau’n gyntaf bob tro.

• Amcangyfrifa’n gyntaf a gwirio wedyn – mae’n syniad da amcangyfrif yr ateb yn gyntaf. A chofia wirio dy ateb go iawn.

• Mae tynnu’n groes i adio. Felly mae hi bob amser yn bosib gwirio ateb swm tynnu drwy adio. Gwiria fod 182 - 37 = 145 drwy wneud y swm: 145 + 37 = 182

Gwylia am y geiriau hyn mewn problemau:

• tynnu i ffwrdd
• gwahaniaeth
• llai na
• minws
• lleihau
• cwtogi

Maen nhw i gyd yn arwydd o swm tynnu.

If the numbers are too high or too difficult to subtract in your head, write them down in columns. Separate the numbers into ones, tens, hundreds and thousands. List the numbers in a column and always start with the ones first.

• Estimate first and check afterwards - it's a good idea to estimate a rough answer first. And always check your actual answer.

• Subtraction is the opposite to addition. So subtraction can always be checked by adding. Check that 182 - 37 = 145 by doing the sum: 145 + 37 = 182

Look out for these words in problems:

• take away
• difference
• less than / fewer than
• minus
• decrease
• reduce

They all indicate subtraction.

Gweithgaredd 1 / Activity 1

Cwblha’r hafaliad. 48 - 21

Complete the equation. 48 - 21

Gweithgaredd 2 / Activity 2

Datrysa'r broblem tynnu.

Solve the subtraction problem.