#### Parent Mathing Tip #9: Shapes

These tips give parents ideas for math exercises that will develop their child's math abilities. Today’s parent tip for “mathing” with your child focuses on shapes.

Cake, decorations, family, and friends — who doesn’t love a good birthday celebration? Every 365 days, each one of us gets the opportunity to celebrate another trip around the sun. And whether we’re counting candles or figuring out how long it will take us to put up streamers and balloons, there are tons of opportunities to use math.

This week’s word problems help kids see that math can be part of their birthday preparations. Look below and choose the one that’s the right skill level for your child. Have them give it a try. And when they feel they’ve found the answer, check their solution against ours.

Questions

**Lower Elementary:**

*Question:* Margie and Carrie are twins. Margie was born on December 17 at 11:45 PM, and Carrie was born on December 18 at 12:07 AM. How much older is Margie than Carrie?

**Upper Elementary:**

*Question:* Barb’s birthday cake has 1 more candle than the number of years she has been alive. If 1/2 of the candles are blue, 1/3 of the candles are green, and the remaining 4 candles are yellow, then how old is Barb?

**Middle School:**

*Question:* Jenny is making a number of treat bags for her birthday party guests. She buys a bag of 50 lollipops, 8 of which are blue raspberry-flavored. Before distributing the lollipops amongst the treat bags, Jenny randomly picks 3 lollipops to keep for herself. Whatever she picks, she keeps. What is the probability that all 3 lollipops Jenny picks are blue raspberry-flavored? Round your answer to the nearest hundredth of a percent.

**High School and Up:**

*Question:* Nick, Rose, and Leif are decorating for their friend Angie’s surprise party. Nick can put up decorations in 1.5 hours, Rose can put up decorations in 2 hours, and Leif can put up decorations in 3.5 hours. How long will it take them to put up decorations if they all work together? Round your answer to the nearest minute.

Solutions

Excellent! Are you ready to check your child’s answer? Look below to see if their solution matches ours.

**Lower Elementary:**

*Answer:* 22 minutes older

*Solution:* The date changes from December 17 to December 18 at 12:00 AM. There are 60 minutes in an hour, and 45 minutes is 15 minutes away from 60 minutes, so Margie was born 15 minutes before midnight. 7 minutes later is when Carrie was born, so Margie is 15 minutes + 7 minutes = 22 minutes older than Carrie.

**Upper Elementary:**

*Answer:* 23 years old

*Solution:* In order to compare the fractional parts, we need to give them the same denominator – in this case, 2 × 3 = 6. 1/2 × 3/3 = 3/6 of the candles are blue, and 1/3 × 2/2 = 2/6 of the candles are green. This means that 3/6 + 2/6 = 5/6 of the candles are blue or green, leaving 1 – 5/6 = 1/6 of the candles yellow. If 1/6 of the candles is the same as 4 candles, then the whole number of candles must be 6 × 4 = 24. If there is 1 more candle on the cake than the number of years Barb has been alive, then she is 24 – 1 = 23 years old.

**Middle School:**

*Answer:* 0.29%

*Solution:* The probability that the first lollipop Jenny picks will be blue raspberry-flavored is 8 lollipops out of 50 total lollipops = 8/50 = 4/25. If she picks this flavor, then the probability of the second lollipop being the same flavor is 8 – 1/50 – 1 = 7/49 = 1/7. If she picks this flavor for the first and the second, then the probability of the third lollipop being the same flavor is 7 – 1/49 – 1 = 6/48 = 1/8. The probability of all of these events occurring is 4/25 × 1/7 × 1/8 = 4/1,400 ≈ 0.29%.

**High School and Up:**

*Answer:* 41 minutes

*Solution:* We need to combine Nick’s, Rose’s, and Leif’s decorating rates by addition. Choosing a common denominator, Nick’s rate is 1/1.5 = 28/42, Rose’s is 1/2 = 21/42, and Leif’s is 1/3.5 = 12/42. Their combined rate of decorating is 28/42 + 21/42 + 12/42 = 61/42, or 61 parties in 42 minutes. To find their combined rate for 1 party, we set 61/42 equal to 1/x (1 party in x minutes). Using cross products, we find that x = 42/61 of an hour = 42/61 of 60 minutes = 42/61 × 60 minutes ≈ 41 minutes.

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