Les statistiques montrent qu’une petite somme d’argent suffit souvent pour changer l’humeur de quelqu’un.

In French, the verb must agree in number with the subject.

• Les statistiques is plural (like the statistics in English), so the verb must be plural: montrent.
• The singular would be la statistique → la statistique montre.

So:

• Les statistiques montrent… = The statistics show…
• La statistique montre… = The statistic shows…

In French, common countable nouns almost always need an article; you can’t usually leave it out as in English.

• Les statistiques with les (definite article) is the usual way to talk in general about statistics as a body of data or knowledge.
• Saying statistiques montrent without an article is ungrammatical in standard French.

Alternatives you might see:

• Les statistiques montrent que… (most natural)
• Selon les statistiques, … (according to the statistics, …)

Qu’ is just que (meaning that) with elision.

• Que becomes qu’ in front of a word that begins with a vowel sound or mute h, to make pronunciation smoother:
  • que une → qu’une
  • que il → qu’il
  • que elle → qu’elle

So qu’une literally = que une (that a), but written and pronounced as one unit: qu’une.

Because somme is a feminine noun in French.

• une somme = a sum / an amount
• Feminine adjectives and determiners must agree:
  • une petite somme (feminine: une, petite)
  • not un petit somme (masculine, incorrect)

Compare:

• un petit problème (masculine)
• une petite somme (feminine)

You just have to memorize the gender of somme as feminine.

Both refer to a small quantity of money, but the nuance is different.

• une petite somme d’argent

  • Treats money as a specific amount (a sum) that could be counted or named.
  • Sounds a bit more formal or objective, often used in writing or when talking about amounts in a more measured way.
  • Can suggest: not a lot, but still a real, concrete sum.

• un peu d’argent

  • Literally: a little money / some money.
  • More vague and informal; focuses on small quantity rather than the idea of a defined sum.

In this sentence, une petite somme d’argent matches the idea that even a relatively small amount (e.g., a bonus, a small gift, a tip) can change someone’s mood.

After a noun of quantity like une somme, beaucoup, peu, etc., French uses de (or d’ before a vowel sound), not de + article.

• Pattern:
  
  • une somme d’argent
  • beaucoup d’argent
  • un kilo de pommes
  • un verre de vin

So:

• une petite somme d’argent (correct)
• une petite somme de l’argent (incorrect in this meaning)

We use d’ because argent begins with a vowel sound: de + argent → d’argent.

In French, many common adverbs (like souvent, toujours, rarement) typically go after the conjugated verb in simple tenses:

• suffit souvent = often suffices / is often enough
• vient souvent = often comes

Other possible positions are:

1. At the beginning of the clause (more emphasis on the frequency):

   • Souvent, une petite somme d’argent suffit pour changer…
     → Often, a small amount of money is enough to change…

2. Very occasionally after the entire verb phrase, but that can sound less natural or slightly more literary in a sentence like this.

   • Une petite somme d’argent suffit pour changer l’humeur de quelqu’un, souvent. (adds often as an afterthought)

In your sentence, suffit souvent is the most neutral and natural placement.

The structure is:

• suffire pour + infinitive = to be enough to + verb

So:

• une petite somme d’argent suffit pour changer l’humeur…
  → a small amount of money is enough to change the mood…

Common patterns with suffire:

• suffire pour faire quelque chose
  • Ça suffit pour vivre. = That’s enough to live on.
• suffire à quelqu’un / à quelque chose
  • Ça lui suffit. = That’s enough for him / her.
  • Ce salaire suffit à notre famille. = This salary is enough for our family.

Here we want “enough to change”, so pour + infinitive is the right pattern.

After pour (meaning for / in order to), French uses a bare infinitive — no de, no à:

• pour changer = (in order) to change
• pour comprendre = to understand
• pour réussir = to succeed

So the correct patterns are:

• suffit pour changer (correct)
• suffit pour de changer (incorrect)
• suffit à changer is not a standard way to express this idea; we normally say suffire pour + infinitive.

Again, this is elision:

• The noun humeur is feminine:
  • la humeur in theory
• But la becomes l’ in front of a vowel sound or mute h:
  • la humeur → l’humeur
  • la amie → l’amie
  • la eau → l’eau

So:

• l’humeur = the mood
• Written with an apostrophe to show the dropped vowel.

French doesn’t have the apostrophe-s possessive like English. Instead, it usually uses de + person:

• l’humeur de quelqu’un = someone’s mood
• le livre de Marie = Marie’s book
• la maison de mes parents = my parents’ house

Using à can express possession in some fixed patterns, especially with body parts or personal belongings, but here de is the normal choice:

• changer l’humeur de quelqu’un (natural)
• changer l’humeur à quelqu’un sounds odd; you might hear ça lui a changé l’humeur, but that’s a different structure (with an indirect object pronoun lui).

So de is the standard “of/’s” marker in this context.

Quelqu’un is an indefinite pronoun meaning someone / somebody.

• It is written as one word with an apostrophe: quelqu’un
• You should not normally write quelque un as two words (except in very rare, special emphatic or poetic uses).

The apostrophe is historical; synchronically you can just remember:

• quelqu’un = someone
• quelque chose = something
• quelques (plural adj.) = some, a few (e.g. quelques personnes = a few people)

So l’humeur de quelqu’un literally = the mood of someone → someone’s mood.